Authentic
graded by Al-Albani
Mishkat al-Masabih 1135
Narrator:Abdullāh ibn ‘Umar
وَعَنِ ابْنِ عُمَرَ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَأْمُرُنَا بِالتَّخْفِيفِ وَيَؤُمُّنَا ب (الصافات) رَوَاهُ النَّسَائِيّ
Ibn ‘Umar said:
God's Messenger used to command us to be brief, and he would recite as-Saffat (Al-Qur’an; 37) when he was our imam. Nasa’i transmitted it.
Cited in Mishkat al-Masabih (No. 1135).