What is the ruling on continuing a supererogatory prayer already started when the Iqamah for the obligatory prayer is called?
Chapter on Facing the Qiblah
Al-Mughni
Book of Prayer
Primary text
If the Iqamah is called while one is performing a supererogatory prayer and one does not fear missing the congregation, one must complete the prayer one has started and must not cut it short, due to the divine command: {And do not invalidate your deeds} (Quran 33:33). Evidence of disapproval for praying when the Iqamah is called includes the narration from 'Aishah where the Prophet (PBUH) saw people praying after the Iqamah and asked, "Two prayers combined?" Similar reports from Anas, Abdullah ibn Sarjas, Ibn Buhaynah, and Abu Hurairah affirm this strong disapproval.
Supporting text
If one fears missing the congregation while performing a supererogatory prayer after the Iqamah, there are two recorded views. One view maintains that one should complete the prayer based on the prohibition of invalidating one's deeds. The second view holds that one should cut the prayer short, as the reward gained from joining the congregation is greater and superior to the reward of completing the partial supererogatory prayer, given that the congregational prayer is valued twenty-seven degrees higher than a man's prayer alone.