Validity of prayer when a single person stands alone behind the row
Chapter on Imamate and Congregational Prayer
Al-Mughni
Book of Prayer
Primary text
The prayer of one who stands alone behind the row for a complete unit of prayer (a full *rak'ah*) is not valid. This is the position of Al-Nakh'i, Al-Hakam, Al-Hasan ibn Salih, Ishaq, and Ibn Al-Mundhir. The evidence is the hadith where the Prophet (peace be upon him) commanded a man praying alone behind the row to repeat the prayer, and another narration where the Prophet told him to restart his prayer, stating there is no prayer for one standing alone behind the row.
Supporting text
Hasan, Malik, Al-Awza'i, Al-Shafi'i, and the proponents of opinion permitted it, citing Abu Bakrah who bowed briefly in front of the row, and the Prophet did not order him to repeat. They also argue that since a woman's position behind the row is valid, a man's should be similar when alone. However, the Prophet's command to repeat invalidates this analogy, and the excuse for Abu Bakrah's action was his ignorance of the prohibition, whereas an established prohibition necessitates invalidity.