Hadith 807:6
Rawh narrated to us, Shu'bah narrated to us, he said: I heard Anas ibn Sirin, he said: I heard 'Abd al-Malik ibn al-Minhal narrating from his father, he said—and he was one of the companions of the Messenger of Allah, may Allah bless him and grant him peace—he said: The Messenger of Allah, may Allah bless him and grant him peace, used to command us to fast the three white days, and he would say: "They are the fasting of a lifetime."
حدثنا روح، حدثنا شعبة، قال: سمعت أنس بن سيرين، قال: سمعت عبد الملك بن المنهال، يحدث عن أبيه، قال:، وكان من أصحاب رسول الله صلى الله عليه وسلم، قال: كان رسول الله صلى الله عليه وسلم يأمرنا بصيام أيام البيض الثلاثة، ويقول: " هن صيام الدهر "