Musnad Ahmad 1297:2

Waki’ narrated to us, he said: Shu’bah narrated to us, from Habib ibn Zayd al-Ansari, from a woman who is called Layla, from Umm ‘Umarah, she said: The Messenger of Allah (may Allah bless him and grant him peace) came to us, so we brought food near to him. Some of those who were with him were fasting. The Prophet (may Allah bless him and grant him peace) said: "When food is eaten in the presence of a fasting person, the angels pray for him."