Talmud for Menachot 81:19

Ẓizith [of a ṭallith used as a shroud] upon a corpse should not be undone.²⁵The removal of the zizith would be an insult to the dead, which is condemned in Prov. 17, 5, Whoso mocketh the poor blasphemeth his Maker, and a dead man is the poorest of all. Abba Saul b. Boṭhnith said, ‘My father told me, “When I die, undo the zizith [in my ṭallith] because they come within the category of holiness”‘.²⁶And should be undone before the ṭallith is used as a shroud. The Sages said: It does not come within the category of holiness, so one may use it as a shroud for the dead or as a pack-saddle for an ass.