פירוש על ברכות 32:8

The laws of mourning (here abelut, the mourning before the burial, which is stricter than abelut, mourning after burial) are derived from Deut. xxvi. 14. Being a Pentateuchal ordinance, how could he set them aside for the personal reason he gives ?

This verse relates to a time of mourning, and it mentions only "a bitter day" ; from this he deduced that the "bitterness" does not apply in the night.