What is the ruling on praying in the second row when the first row is not complete?

Praying in the second row before the first row is complete is contrary to the Sunnah, and the one who does so should not repeat it, even though their prayer is valid. The Messenger of Allah, peace and blessings be upon him, commanded completing the first row, then the one after it, and forbade leaving gaps in the rows, because they are a means for Satan to enter.