From the work “Who Is Alexandre Grothendieck? Volume 3: Spirituality (1970-1991)” by Winfried Scharlau, translated from the German by Melissa Schneps. I quote a passage from “Chapter 1. The Great Turning Point”:
To get a balanced picture, one must add that also Grothendieck’s everyday life was altered by the “great turning point.” From then on he no longer inhabited the bourgeois world where in any case he had always felt himself to be a stranger, and in which he had never really been more than a guest. When he spent the night with friends, he refused to sleep in a bed, but instead rolled himself up in a sleeping bag which he would spread out on the stone floor. Even at home he did not sleep in a bed, but on a door removed from its hinges - he said that this reminded him of his youth in the internment camp. For health reasons he fasted one day a week, and often twice in order to express solidarity, for example with miners in Chile. In any case he lived on a highly reduced diet. During meals with friends and acquaintances he annoyed the wives by lecturing on the chemicals with which their food was probably contaminated. He trudged through the snows of the Canadian winter barefoot in sandals. When a serious accident on a motorbike rendered an operation necessary he refused anesthesia and opted for acupuncture. His atavistic “Jewish avarice” (his own words) broke through, but he dispensed gifts of money right and left with the greatest generosity. Money meant nothing to him, and he reduced his own needs to almost nothing. He switched off the electricity and there was no running water in his house, but it stood open to all and sundry. His cars were the oddest of vehicles; one was a hearse that had served its time, another one had holes in the bottom plate, so that one had to be careful not to let one’s feet poke through onto the road. He failed his driving test nine times and drove for years without a license.
The work is available at Who Is Alexandre Grothendieck?.