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
← Previous Hadith 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 Next Hadith → Did you observe fast in the middle of this month. i. e. Sha'ban? He said: No. Thereupon he said to him: When it is the end of Ramadan, then observe fast for one day or two (Shu'ba had some doubt about it) but he said: I think that he has said: two days.

Sahih Muslim Book 13, Hadith 259