What is the ruling on performing optional (Nafl) prayers when a mandatory (Fard) prayer is outstanding?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
It is disliked (Makruh) for one to perform another voluntary prayer when a mandatory prayer is outstanding. The ruling for fasting is similar; one should not voluntarily fast while having an obligatory fast outstanding. However, if one performs the voluntary act, it remains valid based on the hadith of Ibn 'Umar concerning one who forgets a mandatory prayer and only remembers it behind the Imam; the Prophet confirmed the validity of that performance.
Supporting text
The making up of the established Sunan al-Rawatib (regular Sunnah prayers) is not disliked before the Fard prayer, similar to the ruling regarding the two rak'ahs of Fajr Sunnah.