Musnad Ahmad 32:1482

'Ali ibn 'Asim narrated to us, 'Ubayd Allah ibn Abi Bakr ibn Anas informed us, he said: I heard Anas ibn Malik saying: "The Messenger of Allah, peace and blessings of Allah be upon him, never went out on the day of Fitr until he had eaten some dates." He said: "And Anas used to eat three before he went out, and if he wanted to increase, he would eat five, and if he wanted to increase, he would eat an odd number."