Did you fast in the middle of Sha'ban? He said: No. Thereupon he (the Holy Prophet) said: If you did not observe fast, then you should observe fast for two days.
Sahih Muslim Book 13, Hadith 257
← Previous Hadith It is (the day) when I was born and revelation was sent down to me.

Sahih Muslim Book 13, Hadith 256 Next Hadith → Did you observe any fast in the middle of this month (Sha'ban)? He said: No. Thereupon the Messenger of Allah (ﷺ) said: Fast for two days instead of (one fast) when you have completed (fasts of) Ramadan.

Sahih Muslim Book 13, Hadith 258