Reference for Taanit 26:5

איכא דאמרי אמר רבא אבל אסור בצונן כל שבעה מאי שנא מבשר ויין התם לפכוחי פחדיה הוא דעביד

The answer is, in his case one bereavement followed close on the other. For it has been taught: Where a man suffers one bereavement close upon another and his hair weighs heavy upon him he may thin them out with a razor and he may also wash his clothes in water. R'Hisda said: With a razor, but not with scissors, In water, but not in natron, nor in sand nor in aloe.

Jastrow