Mishkat al-Masabih 4 Prayer كتاب الصلاة 552

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.