Full Sharh — Mishkat al-Masabih 1946
وَعَنْ عِمْرَانَ بْنِ حُصَيْنٍ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: أَنَّهُ سَأَلَهُ أَوْ سَأَلَ رَجُلًا وَعِمْرَانَ يَسْمَعُ فَقَالَ: «يَا أَبَا فُلَانٍ أَمَا صُمْتَ مِنْ سَرَرِ شَعْبَانَ؟» قَالَ: لَا قَالَ: «فَإِذَا أَفْطَرْتَ فَصُمْ يَوْمَيْنِ»
English Translation
‘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.)
Source
Mishkat al-Masabih(مشكاة المصابيح)
Fasting
Hadith Number
1946