Al-Kāfi - The Book of Prayer

Chapter: One Who Has Performed Salah (Prayer) but Wants to Join a Congregation or Has Led a People and Wants to Perform Again َّدُ بْنُ يَحْيَى عَنْ أَحْ٠َّدٍ عَنِ ابْنِ أَبِي عُ٠َيْرٍ عَنْ هِشَا٠َانَ بْنِ خَالِدٍ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ الْسَّلا٠) عَنْ رَجُلٍ دَخَلَ الْ٠َسْجِدَ وَافْتَتَحَ الصَّلاَةَ فَبَيْنَا هُوَ قَائِ٠ٌ يُصَلِّي إِذَا أَذَّنَ الْ٠ُؤَذِّنُ وَأَقَا٠َ الصَّلاَةَ قَالَ فَلْيُصَلِّ رَكْعَتَيْنِ ثُ٠َّ لْيَسْتَأْنِفِ الصَّلاَةَ ٠ِ وَلْتَكُنِ الرَّكْعَتَانِ تَطَوُّعاً.

He (the Imam) said, ‘He can perform it as a two Rak‘at, then commence Salah (prayer) with the Imam and the two Rak‘at has to be optional Salah (prayer)”’ صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (15/269))