Report entitled "Resettlement of Jews" written by SS-Sturmbannführer Gricksch for SS-Col. von Herff and Reichsführer-SS Himmler, after inspection of Auschwitz camp on 14-16 May 1943.
Hitler and the Final Solution - G. Fleming, University of California Press, 1984, p. 142-143:

The Auschwitz camp plays a special role in the resolution of the Jewish question. The most advanced methods permit the execution of the Führer-order in the shortest possible time and without arousing much attention. The so-called "resettlement action" runs the following course: The Jews arrive in special trains (freight cars) toward evening and are driven on special tracks to areas of the camp specifically set aside for this purpose. There the Jews are unloaded and examined for their fitness to work by a team of doctors, in the presence of the camp commandant and several SS officers. At this point anyone who can somehow be incorporated into the work program is put in a special camp. The curably ill are sent straight to a medical camp and are restored to health through a special diet. The basic principle behind everything is: conserve all manpower for work. The previous type of "resettlement action" has been thoroughly rejected, since it is too costly to destroy precious work energy on a continual basis.

The unfit go to cellars in a large house which are entered from outside. They go down five or six steps into a fairly long, well-constructed and well-ventilated cellar area, which is lined with benches to the left and right. It is brightly lit, and the benches are numbered. The prisoners are told that they are to be cleansed and disinfected for their new assignments. They must therefore completely undress to be bathed. To avoid panic and to prevent disturbances of any kind, they are instructed to arrange their clothing neatly under their respective numbers, so that they will be able to find their things again after their bath. Everything proceeds in a perfectly orderly fashion. Then they pass through a small corridor and enter a large cellar room which resembles a shower bath. In this room are three large pillars, into which certain materials can be lowered from outside the cellar room. When three- to four-hundred people have been herded into this room, the doors are shut, and containers filled with the substances are dropped down into the pillars. As soon as the containers touch the base of the pillars, they release particular substances that put the people to sleep in one minute. A few minutes later, the door opens on the other side, where the elevator is located. The hair of the corpses is cut off, and their teeth are extracted (gold-filled teeth) by specialists (Jews). It has been discovered that Jews were hiding pieces of Jewelry, gold, platinum etc., in hollow teeth. Then the corpses are loaded into elevators and brought up to the first floor, where ten large crematoria are located. (Because fresh corpses burn particularly well, only 50-100 lbs. of coke are needed for the whole process.) The job itself is performed by Jewish prisoners, who never step outside this camp again.

The results of this "resettlement action" to date: 500,000 Jews. Current capacity of the "resettlement action" ovens: 10,000 in 24 hours.

Notes From Diary of SS-Doctor Kremer, while in Auschwitz.
'The Good Old Days' - E. Klee, W. Dressen, V. Riess, The Free Press, NY, 1988, p. 256-268:

2 September 1942

3.00 a.m. attended my first Sonderaktion. Dante's Inferno seems to me almost a comedy compared to this. They don't call Auschwitz the extermination camp for nothing!

[Sonderaktion = special action, meaning extermination; in this case, gassing. See, for instance, two following documents.]

5 September 1942

In the morning attended a Sonderaktion from the women's concentration camp (Muslims); the most dreadful of horrors. Hschf. Thilo -- army doctor -- was right when he said to me this is the 'anus mundi'. In the evening towards 8.00 attended another Sonderaktion from Holland.

['Muslims' does not mean "practicing Islam;" this is the way the SS referred to emaciated people.]

10 October 1942

Extracted and fixed fresh live material from liver, spleen and pancreas....

11 October 1942

Today, Sunday, there was roast hare for lunch--a real fat leg--with dumplings and red cabbage for 1.25 RM.

12 October 1942

Second inoculation against typhus, later on in the evening severe generalized reaction (fever). Despite this in the night attended a further Sonderaktion from Holland (1,600 persons). Ghastly scenes in front of the last bunker! That was the 10th Sonderaktion.

13 November 1942

Extracted fresh live material (liver, spleen and pancreas) from a previously photographed, severely atrophied Jewish prisoner aged eighteen. Fixed as always, liver and spleen in Carnoy and pancreas in Zenker (Prisoner No. 68,030).

Letter from SS-Obersturmbannführer Rodl to the inspector of concentration camps, SS-Obersturmbannführer Liebehenschel, 14 November 1941.
Hitler and the Final Solution - G. Fleming, University of California Press, 1984, p. 99:

The Commandant's office has submitted to date two lists recommending the conferment of the Kreigverdienstkreuz [war service cross]. In both of these appear SS personnel who participated in executions. We herewith request confirmation as to whether these names should be listed once again in the roll currently under preparation. Further requested is information as to whether in the recommendation lists under "reasons and comments of immediate superior" there should be specified "execution, i.e., special action" or whether a general, routine reason should be given.

Letter from Bischoff, head of construction management at Auschwitz, to the SS economic and administrative head office in Berlin, regarding construction at Auschwitz, 13 October 1942.
Auschwitz: Technique and operation of the gas chambers - J.C Pressac, the Beate Klarsfeld Foundation, NY, 1989, p. 198:

As regards the construction of the new crematorium building, it was necessary to start immediately in July 1942 because of the situation caused by the special actions.

Letter from SS-Sturmbannführer Bischoff, of the Auschwitz construction department, to SS General Kammler, January 29, 1943.
The Final Solution: The Attempt to Exterminate the Jews of Europe, 1939-1945 - G. Reitlinger, South Brunswick, T. Yosellof, 1968, p. 158-159:

Crematorium No. 2. The completed furnaces have been started up in the presence of Engineer Prufer from Messers. Topf (of Erfurt). The planks cannot yet be moved from the ceiling of the mortuary cellar on account of frost, but this is not important, as the gassing cellar can be used for that purpose. The ventilation plant has been held up by restrictions on rail transport, but the installation should be ready by February 20th.

Letter from SS-Sturmbannführer Bischoff, March 6 1943.
Auschwitz: Technique and operation of the gas chambers - J.C Pressac, the Beate Klarsfeld Foundation, NY, 1989, p. 434:

... order of 6/3/1943 concerning the delivery of a gas tight door 100 x 192 cm for cellar I of Krematorium III, to be produced to the identical pattern and dimensions as the cellar door of Krematorium II which is situated opposite, with peephole of double 8 mm glass, with rubber sealing strip and frame.

Letter from SS-Sturmbannführer Jahrling to SS-General Kammler estimating the number of corpses that can be disposed off in 24 hours in the Auschwitz crematoriums, June 25 1943.
Auschwitz: Technique and operation of the gas chambers - J.C Pressac, the Beate Klarsfeld Foundation, NY, 1989, p. 247:

1.) Crematorium I ~~~~~~~~~~~~~~~
3 x 2 muffles	340 persons

2.) Crematorium II ~~~~~~~~~~~~~~~
5 x 3 muffles	1440 persons

3.) Crematorium III ~~~~~~~~~~~~~~~
5 x 3 muffles	1440 persons

4.) Crematorium IV ~~~~~~~~~~~~~~~
8 muffles	768 persons

5.) Crematorium V ~~~~~~~~~~~~~~~
8 muffles	768 persons

A letter asking for a truck to bring Zyklon-B to Auschwitz; uses the standard camouflage term "resettlement of Jews" to refer to extermination. Another such document asks for "material for special treatment" - another term used to disguise extermination.
Auschwitz: Technique and operation of the gas chambers - J.C Pressac, the Beate Klarsfeld Foundation, NY, 1989, p. 557:

Radio message 13 SS Garrison Radio Station Auschwitz Origin WVHA [SS economic administration head office]

Received 2nd October 1942 in the Kommandantur of Auschwitz Concentration camp

The movement authorization for one 5 Ton truck with trailer to Dessau and back in order to pick up material for the resettlement of the Jews, is hereby accorded.

The authorization is to be given to the driver.

Liebehenschel
SS Lieutenant Colonel
Permanent representative of the head
of the service with the rank of Waffen SS
Lieutenant General

For file

Head of the radio station

Letter from SS-Sturmbannführer Jahrling to Topf & Sons, March 6 1943.
Auschwitz: Technique and operation of the gas chambers - J.C Pressac, the Beate Klarsfeld Foundation, NY, 1989, p. 221:

[This document is interesting for two reasons: first, it demonstrates that the underground cellars in the crematoriums could not have possibly been morgues, as morgues are never heated; heating, however, does facilitate the evaporation of Zyklon-B. Also, the document - like many others - makes reference to an "undressing room," and there is no reason for a morgue to have one near by. Pressac contains numerous other documents attesting to the design and use of the Auschwitz gas chambers. Even the fake shower heads are mentioned.]

Subject: KL Auschwitz Krematorien II and III

In accordance with your suggestion, the service agrees that cellar 1 should be preheated with the air coming from the rooms of the 3 forced draught installations. The supply and installation of the ductwork and blowers necessary to this end are to be effected as soon as possible. As you point out in your above-mentioned letter, execution should commence this week. We would ask you to send in triplicate detailed quote for supply and installation.

At the same time, we would ask you to send an additional quotation for the modification of the air-extraction installation in the undressing room.

Sources: Shamash. the comments inside the square brackets were written by Daniel Keren for the Shamash archives.

Nazi Collaborations with Businesses: Corporate Involvement in Concentration Camps