Sahih Muslim , Book 4, Hadith 1417 (USC-MSA) ⓘ
Abu Sa'id al-Khudri reported Allah's Messenger as saying: When there are three persons, one of them should lead them. The one among them most worthy to act as Imam is one who is best versed in the Qur'an.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا كَانُوا ثَلاَثَةً فَلْيَؤُمَّهُمْ أَحَدُهُمْ وَأَحَقُّهُمْ بِالإِمَامَةِ أَقْرَؤُهُمْ " .
also referenced under: Book 5, Hadith 365 (In-Book) & Hadith 672 (Reference)