Chapter on the Rulings of Congregational Prayer (the Minimum Number for Congregational Prayer, the Description of the Imam, Who Is to Be Followed and Who Is Not to Be Followed, Recitation Behind Both of Them, the Rulings of Those Led in Prayer, and Other Such Rulings Related to It)

Tahdhīb al-Aḥkām|Volume 3|Book 1|Chapter 3

Tahdhīb al-Aḥkām

Volume 3, Book 1, Chapter 3

Chapter on the Rulings of Congregational Prayer (the Minimum Number for Congregational Prayer, the Description of the Imam, Who Is to Be Followed and Who Is Not to Be Followed, Recitation Behind Both of Them, the Rulings of Those Led in Prayer, and Other Such Rulings Related to It)

Hadith #88

مُحَمَّدُ بْنُ يَعْقُوبَ عَنْ مُحَمَّدِ بْنِ إِسْمَاعِيلَ عَنِ اَلْفَضْلِ بْنِ شَاذَانَ وَ عَلِيِّ بْنِ إِبْرَاهِيمَ عَنْ أَبِيهِ جَمِيعاً عَنِ اِبْنِ أَبِي عُمَيْرٍ عَنْ حَفْصِ بْنِ اَلْبَخْتَرِيِّ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: فِي اَلرَّجُلِ يُصَلِّي اَلصَّلاَةَ وَحْدَهُ ثُمَّ يَجِدُ جَمَاعَةً قَالَ« يُصَلِّي مَعَهُمْ وَ يَجْعَلُهَا اَلْفَرِيضَةَ»

Muhammad ibn Yaqub from Muhammad ibn Ismail from al-Fadl ibn Shadhan, and Ali ibn Ibrahim from his father, all from Ibn Abi Umayr from Hafs ibn al-Bukhturi from Abu Abdillah , peace be upon him: Imam al-Sadiq said regarding a man who performs the prayer alone, then finds a group (praying in congregation). Imam said: “He should pray with them and count it as the obligatory prayer.”

Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 3, p. 56