Sayyiduna Kahmas al-Hilali (may Allah be pleased with him) said: I came to the Messenger of Allah (peace and blessings be upon him) and stayed with him (peace and blessings be upon him) for some time, then went back. A year later I came again and said: O Messenger of Allah, do you not recognise me? He (peace and blessings be upon him) said: "No." I said: I am the one who was with you last year. He (peace and blessings be upon him) said: "Then what has brought about this change in you?" I said: Since I parted from you I have not eaten anything during the day. He (peace and blessings be upon him) said: "Who ordered you to torment yourself? Fast one day of the middle days of the month." I said: Tell me more. He (peace and blessings be upon him) told me more, until he said: "Fast three days of the month."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16484