"The Messenger of Allah ﷺ came out to us and said:'Will you not form rows as the angels form rows before their Lord? They said: 'How do the angels form rows before their lord? He said: 'They complete the first row and fill the gaps in the rows."' (Using translation from Nasāʾī 816)   

خَرَجَ رَسُولُ اللهِ ﷺ إِلَى الصُّفُوفِ فَقَالَ أَلَا تَصُفُّونَ كَمَا تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهِمْ؟ قَالُوا وَكَيْفَ تَصُفُّ الْمَلَائِكَةُ عِنْدَ رَبِّهِمْ؟ قَالَ يُتِمُّونَ الصُّفُوفَ الْمُقَدَّمَةَ وَيَتَرَاصُّونَ فِي الصَّفِّ  

[Machine] The Messenger of Allah said, "Complete the first row, then the second, even if there is a deficiency in the back rows. He used to say, 'The best rows for men are the front rows, and the best rows for women are the back rows.'"  

قَالَ رَسُولُ اللهِ ﷺ أَتِمُّوا الصَّفَّ الْأَوَّلَ ثُمَّ الثَّانِي وَإِنْ كَانَ نَقْصٌ كَانَ فِي الْمُؤَخَّرِ وَكَانَ يَقُولُ خَيْرُ صُفُوفِ الرِّجَالِ أَوَّلُهَا وَخَيْرُ صُفُوفِ النِّسَاءِ آخِرُهَا  

The Prophet ﷺ said: Complete the front row, then the one that comes next, and if there is any incompleteness, let it be in the last row. (Using translation from Abū Dāʾūd 671)   

أَنَّ رَسُولَ اللهِ ﷺ قَالَ أَتِمُّوا الصَّفَّ الْمُقَدَّمَ ثُمَّ الَّذِي يَلِيهِ فَمَا كَانَ مِنْ نَقْصٍ فَلْيَكُنْ فِي الصَّفِّ الْمُؤَخَّرِ