The Messenger of Allah ﷺ prayed over someone in his grave after he had been buried.
حدثنا أبو معاوية حدثنا الشيباني عن الشعبي
أن رسول الله ﷺ صلى على صاحب قبر بعدما دفن
No references are available.
Its isnad is sahih, and its meaning is found in Sahihayn and elsewhere, see al-Muntaqa 1825. Shaybani is Abu Ishaq Sulayman, and it will also come again at 2554.