The Book of Prayer - Friday
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا مُحَمَّدٌ، - وَهُوَ ابْنُ جَعْفَرٍ - حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، قَالَ سَمِعْتُ جَابِرَ بْنَ عَبْدِ اللَّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم خَطَبَ فَقَالَ " إِذَا جَاءَ أَحَدُكُمْ يَوْمَ الْجُمُعَةِ وَقَدْ خَرَجَ الإِمَامُ فَلْيُصَلِّ رَكْعَتَيْنِ " .Jabir b. 'Abdullah said that the Messenger of Allah (ﷺ) delivered the sermon and said:When any one of you comes for the Friday (prayer) and the Imam comes out (from his apartment), (even then) should observe two rak'ahs (of prayer)
From Sahih Muslim, whose reports the scholars accept as authentic.