Explanation of the hadith
The Prophet (ﷺ) commanded the men praying in congregation to complete the first row, then to complete the row behind it, and so on. If there is any deficiency in a row, let that deficiency be in the last row.
عَنْ أَنَسِ بْنِ مَالِكٍ رَضِيَ اللهُ عَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ:
عَنْ أَنَسِ بْنِ مَالِكٍ رَضِيَ اللهُ عَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ: «أَتِمُّوا الصَّفَّ المُقَدَّمَ، ثُمَّ الَّذِي يَلِيهِ، فَمَا كَانَ مِنْ نَقْصٍ فَلْيَكُنْ فِي الصَّفِّ المُؤَخَّرِ».
Anas ibn Mālik (may Allah be pleased with him) reported that the Messenger of Allah (ﷺ) said:
Anas ibn Mālik (may Allah be pleased with him) reported that the Messenger of Allah (ﷺ) said: "Complete the front row first, then the one following it. If there is any deficiency (in the rows), let it be in the last row."
The Prophet (ﷺ) commanded the men praying in congregation to complete the first row, then to complete the row behind it, and so on. If there is any deficiency in a row, let that deficiency be in the last row.