Bulugh al-Maram 2 The Book of Prayer كتاب الصلاة 262

وَلِمُسْلِمٍ عَنْ أَنَسٍ] قَالَ [ : { كُنَّا نُصَلِّي رَكْعَتَيْنِ بَعْدَ غُرُوبِ اَلشَّمْسِ , فَكَانَ – صلى الله عليه وسلم -يَرَانَا , فَلَمْ يَأْمُرْنَا وَلَمْ يَنْهَانَا } 1 1 – صحيح ، رواه مسلم ( 836 ) .

Muslim has reported from Anas (RA) that he said, “We used to pray two Rak’at after sunset and the Prophet (صلى الله عليه وسلم) used to see us, but he neither commanded nor forbade us.”