The prayer of a person praying alone behind the rows is invalid

Q: What is the ruling on the prayer of a person praying alone behind the rows? If someone enters and does not find a place in the row, what should he do? And if he finds a boy who has not reached puberty, should he stand in the row with him?

A: The ruling on praying alone behind the rows is invalidity; because the Prophet (peace and blessings be upon him) said: This indicates that there is no difference between the one who found a gap in the row and the one who did not, in order to block the means to laxity in praying alone behind the rows.
However, if a latecomer arrives and the imam is bowing, and he bows behind the row, then enters the row before prostration, that suffices for him. This is based on what is established in Sahih al-Bukhari (may Allah have mercy on him) from Abu Bakrah al-Thaqafi (may Allah be pleased with him) that he came to the prayer and the Prophet (peace and blessings be upon him) was bowing, so he bowed behind the row, then entered the row. The Prophet (peace and blessings be upon him) said to him after the salam: and did not order him to make up the rak'ah.
As for the one who arrives while the imam is in prayer and does not find a gap in the row, he should wait until someone is found to stand in the row with him, even a boy who has reached the age of seven or more, or he should move forward and stand to the right of the imam, acting in accordance with all the hadiths.
May Allah guide all the Muslims to understanding in the religion and steadfastness upon it, for He is the All-Hearing, the Near.