Sahih al-Bukhari 4996

Abdan related to us, from Abu Hamza, from al-Amash, from Shaqiq, who said: Abdullah said, ‘I know the paired surahs that the Prophet (peace and blessings be upon him) used to recite two by two in each rakah.’ Abdullah stood up, and Alqama went in with him. When Alqama came out, we asked him. He said, ‘They are twenty surahs from the beginning of al-Mufassal, according to Ibn Masud’s arrangement. The last of them are the Hawamim, Ha Mim al-Dukhan, and “About what do they ask one another?”’