Joining Salah while the row is full

A: Anyone who performs one Rak‘ah or more with the Imam (the one who leads congregational prayer) while standing alone behind a row in congregational Salah and no man or discerning child aligns with him, his Salah is invalid. This is based on the general meaning of the saying of the Prophet (peace be upon him), “There is no Salah for the one who prays alone behind the row.” The Messenger of Allah (peace be upon him) saw a man performing Salah alone behind the row and ordered him to repeat the Salah. (Related by Imam Ahmad Al-Tirmidhy - who judged it to be Hadith Hasan [a Hadith whose chain of narration contains a narrator with weak exactitude, but is free from eccentricity or blemish] - and Ibn Majah, through a trustworthy Sanad [chain of narrators]) However, if a man performs Salah standing alone behind a row and another man or even a discerning child joins him before the Imam performs the first Sujud (prostration) of the Rak‘ah that he was joined in, his Salah will be valid, as he will not be alone in this situation. (Part No. 6; Page No. 350) Accordingly, the Salah of a man who performs a complete Rak‘ah with the Imam standing alone behind a row before another person joins him is invalid, based on the two Hadith quoted above. Also, as the Rak‘ah he performed while standing alone is invalid, it is not permissible to base the rest of Salah upon it and it will be obligatory on him to repeat the whole Salah from the beginning.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.