Q: What is the duty of the person who becomes aware during the afternoon prayer that he had not performed noon prayer?
A: If he starts saying the afternoon prayer thinking that he had prayed the noon prayer and during the prayer he notices his mistake, then if that happened at the time which is common between noon and afternoon prayers, he should, immediately, change his intention to the noon prayer and finish it and, then, perform the afternoon prayer. If that happens at the specific time of the noon prayer [which starts at noon time and last until it is enough for offering noon prayer, i.e. enough for four rak‘ahs for the resident person and two rak‘ahs for the traveling one], it will be an obligatory caution to change one’s intention to the noon prayer and complete it, but he should perform both the noon and afternoon prayers later in order. The same duty is applicable to maghrib and ‘ishā’ prayers.