(76) باب صَوْمِ يَوْمٍ وَإِفْطَارِ يَوْمٍ وَذِكْرِ اخْتِلاَفِ أَلْفَاظِ النَّاقِلِينَ فِي ذَلِكَ لِخَبَرِ عَبْدِ
It was narrated that 'Abdullah bin 'Amr said:
"The Messenger of Allah said: "The best of fasting is the fast of Dawud, peace be upon him. He used to fast for one day and break his fast for one day."' 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted."
Reference: Sunan an-Nasa'i 2388
In-book reference: Book 22, Hadith 299
English translation: Vol. 3, Book 22, Hadith 2390