the response is that the text must be understood according to its apparent and immediately understood meaning, unless evidence indicates otherwise. What is immediately understood here is that the Prophet, peace and blessings be upon him, commanded him to repeat the prayer because he had prayed alone behind the row, as the context of the report indicates; and the basic presumption is that there was no other reason.
Accordingly, the preponderant view is that praying alone behind the row is not valid; rather, it is invalid, and one must repeat it. But if someone asks: “Would not the middle position be the preponderant view: that the prayer is valid if there is an excuse?”
The answer is: Yes, the middle position is the preponderant one: if there is an excuse, the prayer is valid. For negating the validity of the prayer of one who stands alone behind the row indicates that joining the row is obligatory, since validity is negated only due to committing something prohibited or omitting an obligation. Thus, it indicates that standing in a row with others is obligatory. The legal principle is that there is no obligation in the case of inability, as Allah Most High says:
“Fear Allah as much as you are able.” [Surah al-Taghabun, 16]
And He says:
“Allah does not burden a soul beyond its capacity.” [Surah al-Baqarah, 286]
Thus, when a worshipper arrives and finds that the row is already complete, there is no place for him in it. In that case, his standing alone is due to an excuse, and his prayer is valid. This is a middle position, and it was the view chosen by Shaykh al-Islam Ibn Taymiyyah, may Allah have mercy on him, and our shaykh, Abd al-Rahman ibn Sa'di. It is the correct view.
If someone asks: “Why do you not say that he should pull someone out of the row?”
The answer is that we do not say this, because it entails several harmful consequences:
The first harmful consequence is that it distracts the person who is pulled back.