Sunan An-Nasa'i

It was narrated that Ibn Al-Malih said:""I entered with Zaid upon 'Abdullah bin Amr and he narrated: 'The Messenger of Allah was told about my fasting, so the entered upon me and I gave him an average-sized leather pillow that was stuffed with palm fibvers. He sat in the ground with the pillow between myself and him, and said: ""Whill it not be sufficient for you to fast three days each months?"" I said: O Messenger of Allah! He said: ""O Messenger of Allah!"" He said: ""Eleven."" I said: ""O Messenger of Allah!"" Then the Prophet said: ""There is not fast better than the fast of Dawud, half of a lifetime, fasting one day and not next