It is narrated from Sayyiduna Abu Dharr (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Whoever among you wishes to fast three days in a month, let him fast on the three days of Ayyam al-Beedh (the white days).
Hadith Referenceالفتح الربانی / كتاب الصيام / 3957