What is the ruling on a person supplicating for the deceased at the time of burial, and on those present saying "Amen" to this supplication?

Supplicating for the deceased after burial is legislated, based on the Hadith narrated by Uthman (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) when he finished burying the deceased, would stand over the grave and say: "Ask Allah for forgiveness for your brother and ask for steadfastness for him, for indeed he is now being questioned." It is not reported that the Prophet (peace and blessings of Allah be upon him) or his companions supplicated in congregation. Rather, he (peace and blessings of Allah be upon him) would supplicate for the deceased individually, saying: "O Allah, forgive him. O Allah, make him steadfast," three times, then depart.