"I heard a freed slave of ours called Laila narrated from Umm Amarah bint Ka'b Al-Ansar, that the Prophet entered upon her and some food was brought to him. He said: 'Eat.' She said: 'I am fasting.' So the Messenger of Allah said: 'Indeed the angels send Salat upon the fasting person when (others) eat in his presence, until they finish.' And perhaps he said: 'Until they have eaten their fill.'"
Jami` at-Tirmidhi Book 8, Hadith 104