Sunan An-Nasai, Chapter: The Book of Purification

that he asked Aisha: "Can a woman eat with her husband while she is menstruating? She said: 'Yes. The Messenger of Allah (saw) would call me to eat with him while I was menstruating. He would take a piece of bone on which some bits of meat were left and insist that I take it first, so I would nibble a little from it, then put it down. Then he would take it and nibble from it, and he would put his mouth where mine had been on the bone. Then he would ask for a drink and insist that I take it first before he drank from it. So I would take it and drink from it, then put it down, then he would take it and drink from it, putting his mouth where mine had been on the cup.'" (Sahih)