Mishkat al-Masabih #1946

‘Imran b. Husain said that the Prophet asked him, or that he asked a man in ‘Imran’s hearing, “Father of so and so, did you not fast the last day of Sha'ban?" When, he replied that he had not, he said, “If you did not observe a fast, you must fast for two days."* *To reconcile this tradition with that of Abu Huraira at the foot of p.420 it is suggested that the man had made a vow to observe this fast, or that it was his custom. (Bukhari and Muslim.)