(38) باب بَيَانِ أَنَّ أَوَّلَ وَقْتِ الْمَغْرِبِ عِنْدَ غُرُوبِ الشَّمْسِ
A hadith like this, i. e." We used to observe evening prayer...." so on and so forth, has been narrated by Rafi' b. Khadij by another chain of transmitters.
Reference: Sahih Muslim 637 b
In-book reference: Book 5, Hadith 278
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1330