Anas (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "Fill (complete) the first row, then the one next to it; and if there is any deficiency (incompleteness), it should be in the last row."[Abu Dawud].
App reference: Book 9, Hadith 103
Arabic/English book reference: Book 9, Hadith 1093