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.
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَهُ أَوْ لآخَرَ أَصُمْتَ مِنْ سَرَرِ شَعْبَانَ قَالَ لاَ قَالَ فَإِذَا أَفْطَرْتَ فَصُمْ يَوْمَيْنِ
The Messenger of Allah ﷺ asked a man: Did you fast the last day of Sha'ban ? He replied: No. He said: If you did not observe a fast, you must fast for a day. One of the two narrators said: For two days. (Using translation from Abū Dāʾūd 2328)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ لَهُ أوَ لِرَجُلٍ أَصُمْتَ مِنْ سَرَرِ شَعْبَانَ شَيْئًا قَالَ لَا قَالَ فَإِذَا أَفْطَرْتَ فَصُمْ يَوْمَيْنِ
[Machine] "That the Prophet ﷺ said to him or to a man, 'Did you observe any fast after mid-Sha'ban?' He said, 'No.' The Prophet ﷺ said, 'Then if you can, observe fast for two consecutive days.'"
أَنَّ النَّبِيَّ ﷺ قَالَ لَهُ أَوْ لِرَجُلٍ صُمْتَ مِنْ سُرَرِ شَعْبَانَ شَيْئًا؟ قَالَ لَا قَالَ فَإِذَا أَفْطَرْتَ فَصُمْ يَوْمَيْنِ