The passage occurs on page 651, in which Gerlach is propounding his (not very well supported) theory that at one stage it was planned to set up a mass extermination centre at Mogilev in Belorussia, to which the Jews of Europe would be shipped.
My translation:Bach-Zelewski erklaerte in Nuernberg gegenueber den Us-Amerikanern, eines Tages zu Anfang des Jahres 1943 (vermutlich frueher) sei bei ihm eine "kleine Kommission" aus Hamburg erschienen, die eben in diesem Zwanfsarbeitslager [in Mogilev] in Himmlers Auftrag eine Gaskammer errichten wollte. Fuer sich genommen, erscheint diese Aussage nicht ernstzunehmen, aber sie passt mit Heydrichs Bemerkung in Prag und der Lieferung des Krematoriums zusammen. Himmler erschien bei seinem Besuch in Mogilew am 23. bis 25. Oktober 1941 aus nicht ersichtlichen Gruenden in Begleitung des HSSPF Nordsee, Querner, mit Dienstsitz in Hamburg und mit "8 andere[n] Herren". Es waere moeglich, dass dies zur Vorbereitung des Besuchs der von Bach-Zelewski angefuehrten "Kommission" diente, die den Bau der Gaskammer vorbereiten wollte. Neue Erkenntnisse von Richard Breitman zeigen Verbindungen zwischen Querner und der Firma Tesch & Stabenow in Hamburg, die kurz darauf Vertreter nach Mogilew und Riga fuer den Einsatz von Zyklon-Gasen entsandte. Allerdigns deuten die von Breitman gefundenen Materialien eher auf die verhaeltnismaessig harmlose Erklaerung hin, dass diese Gase in Mogilew und Riga entsprechend ihrer eigentlichen Funktion zur Desinfektion von Textilien oder Gebaeuden insbesondere der Waffen-SS-Einheiten sowie der POlizei im Mittelabschnitt der Front eingesetzt wurden.
Many readers will know that at the post-war trial of Tesch and Weinbacher, the managers of the firm Tesch & Stabenow, reports of the visit of representatives of the firm to Riga for the purpose of using Zyklon-B was accepted as proof that the firm had knowignly supplied that prodcut to the SS for homicidal purposes.Bach-Zelewski declared in Nuremberg to the Americans that one day toward the beginning of 1943 (in reality presumably earlier) there appeared at his place a "small commission" from Hamburg, which had been commissioned by Himmler to build a gas-chamber in precisely that forced-labour camp [in Mogilev]. Taken by itself, that testimony appears not to be taken seriously, but it corresponds with Heydrich's observation in Prague [on 10 October; he wanted to deport part of the Prague Jews to the camps for communist prisoners run by Einsatzgruppen leaders Nebe and Rasch] and the delivery of the crematorium [to Mogilev]. On Himmler's visit to Mogilev on 23 to 25 October, he was accompanied, for reasons that are not immediately apparent, by the HSSPF North Sea, Querner, with his seat in Hamburg, and with "8 other gentlemen". It is possible that this was preparation for the visit of the "commission" introduced by Bach-Zelewski, which was to prepare the construction of the gas-chamber. New data from Richard Breitman show connections between Querner and the firm Tesch & Stabenow, which shortly afterward despatched representatives to Mogilev and Riga for the deployment of Zyklon-gasses. However, the materials found by Breitman point more to the relatively harmless explanation that these gasses were used in Mogilev and Riga according to their actual function, for the disinfection of textiles or buildings, particularly those of the Waffen-SS units and of the police in the central section of the front.
The British judges who sentenced Tesch and Weinbacher to death may be forgiven for their false interpretation of the visit to Riga. At that time the imaginations of Allied officials were filled with reports of the homicidal use of Zyklon-B. to the extent that the possibility of an innocent use was simply disregarded.
Today we know much more about the normal use of Zyklon-B for delousing (even Gerlach confirms that that was its proper use), so there is no excuse for historians confusing the normal and homicidal uses, and Breitman apparently did.