The third view on this issue is that it is not valid for one praying alone to change into an imam, whether in an obligatory or a voluntary prayer—just as it is not valid for one praying alone to change into a follower, whether in an obligatory or a voluntary prayer. This is the established position of the school (1). Thus, the author’s view here occupies a middle position between the two views.
However, the correct view is that this is valid in both obligatory and voluntary prayers. With regard to voluntary prayer, there is an explicit text establishing it, as mentioned previously. As for obligatory prayer, whatever is established in voluntary prayer is also established in obligatory prayer unless there is evidence to the contrary.
If someone were to ask: How do those who maintain that it is invalid in both obligatory and voluntary prayers respond to the hadith of Ibn Abbas?
The answer is that they reply: The Prophet ﷺ began the prayer alone while it was most likely in his estimation that Ibn Abbas would pray with him. On this basis, they held that if one praying alone changes from praying alone to becoming an imam, and before beginning the prayer he expected that someone would come and pray behind him, this is valid. They said: Since he expected someone to join him, he had intended to be an imam from the beginning of the prayer in its later stage, and this does not invalidate it (2).
They may be answered in two ways:
First: It is far-fetched that the Messenger ﷺ would have expected Ibn Abbas to pray with him when he was a young boy asleep.
Second: Even if this were not far-fetched, who can claim that the Messenger ﷺ expected this? That requires evidence, because