Is it considered a sin to withdraw from the row during prayer to form a new row?

If one prays alone behind the row because there is no space in the row in front of him, then his prayer is valid. However, if he prays alone while there is space available, then his prayer is invalid. It is not permissible for someone who does not find an opening to pull someone from the row to stand with him, because this involves several concerns, including: creating a gap in the row and distracting the worshippers. Nor should someone in the row move back to stand with the one who is praying alone, due to the Prophet's (peace be upon him) saying: "Whoever joins a row, Allah joins him, and whoever cuts off a row, Allah cuts him off."