And from him, from Muhammad ibn Sinan, from Ibn Muskan, from al-Halabi:
Abu Abdillah عليه السلام, peace be upon him, said: "If one forgets to say the salam behind the imam, the salam of the imam suffices for him."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 170