Complete the front row first

Fill the first row, then the next; any gap should be in the last row.

Narrated by Anas ibn Malik

Complete the front row, then the one after it. If there is any shortfall, let it be in the last row.

Sunan Abi Dawud 671

What this hadith teaches

New rows are started only when the one in front is full.

Reference and grade

Grade
Sahih (al-Albani)
Narrator
Anas ibn Malik

The hadith in Arabic نص الحديث

أَتِمُّوا الصَّفَّ الْمُقَدَّمَ ثُمَّ الَّذِي يَلِيهِ فَمَا كَانَ مِنْ نَقْصٍ فَلْيَكُنْ فِي الصَّفِّ الْمُؤَخَّرِ

Arabic text of Sunan Abi Dawud 671, as given on sunnah.com.