Abu Dawud Book 3, Hadith Number 1663.

Narated By Umm Bujayd : She took the oath of allegiance to the Apostle of Allah (PBUH) and said to him: Apostle of Allah, a poor man stands at my door, but I find nothing to give him. The Apostle of Allah (PBUH) said to her: If you do not find anything to give him, put something in his hand, even though it should be a burnt hoof.