He was also asked:

Regarding the Prophet’s saying (may Allah bless him and grant him peace), “The Quran was revealed in seven ahruf (forms),” what is meant by these seven? Do the readings attributed to Nāfi‘, ‘Āsim, and others represent the seven ahruf, or one of them? What caused the reciters to differ over readings accommodated by the script of the Quranic codex? Is it permissible to recite the noncanonical readings transmitted by al-A‘mash, Ibn Muhaysin, and others? If reciting them is permissible, is it also permissible to use them in prayer? Give us your ruling; may Allah reward you.

He answered:

All praise is due to Allah, Lord of all worlds. This is a “major question,” discussed by scholars of various disciplines: jurists, Quranic reciters, specialists in hadith, Quranic exegesis, speculative theology, and the explanation of unfamiliar vocabulary, among others. Indeed, entire works have been devoted to it. Among the most recent such works is that written by Shaykh Abū Muhammad ‘Abd al-Rahmān ibn Ismā‘īl ibn Ibrāhīm al-Shāfi‘ī, known as Abū Shāma, the author of the “Commentary on al-Shātibiyya.”