Is there a specific supplication or words to be recited at the time of burial, or is it sufficient to bury the deceased and then leave?

The Messenger of Allah (peace and blessings be upon him and his family) instructed Muslims to make supplications for the deceased after burial. ʿUthman ibn ʿAffan (may Allah be pleased with him) reported that whenever the Prophet (peace and blessings be upon him and his family) finished burying the deceased, he would stand by the graveside and say, " Seek forgiveness for your brother and pray that he be granted steadfastness, for he is now being questioned" (recorded by Abu Dawud).

It is therefore recommended to make supplications for the deceased after burial. One of those accompanying the funeral who is good at making supplications may stand and say, "In the Name of Allah and according the religion of the Messenger of Allah (peace and blessings be upon him and his family). O Allah, forgive him and grant him steadfastness when he is questioned. O Allah, forgive him, have mercy on him, grant him well-being, pardon him, honor his abode, and make his resting place spacious." Alternatively, the person making the supplication may recite any other appropriate supplications he knows.

And Allah Almighty knows best.