It is narrated from Sayyidah Aishah (may Allah be pleased with her): By Allah! We did not know of his (peace and blessings be upon him) burial until we heard the sound of the spades in the middle of the night of Wednesday.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6727
It is narrated from Sayyiduna Anas (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) fell ill with the illness in which he passed away, Sayyidah Fatimah (may Allah be pleased with her) propped him (peace and blessings be upon him) up against her chest, and spells of faintness began to come over him (peace and blessings be upon him). Sayyidah Fatimah (may Allah be pleased with her) began to say: "Alas! How much pain my dear father is in!" He (peace and blessings be upon him) said: "After today, there will be no pain for your father." When he (peace and blessings be upon him) passed away and was buried, Sayyidah Fatimah (may Allah be pleased with her) said: "O Anas! Did your hearts allow you to pour earth over the Messenger of Allah (peace and blessings be upon him)?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6728
Hisham bin Sa'd narrates from Ziyad, and he from Abu al-Mundhir (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) threw three handfuls of earth into a grave.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6729
Abdullah bin Amir bin Rabi'ah narrates from his father (may Allah be pleased with him): I saw the Prophet (peace and blessings be upon him) when Uthman bin Maz'un (may Allah be pleased with him) was buried. He (peace and blessings be upon him) performed his funeral prayer and said four takbirs over him, and threw earth three times with both his hands while he (peace and blessings be upon him) was standing at the grave.
Its chain is weak, but it has a supporting report through Ja'far bin Muhammad from his father, from the Prophet (peace and blessings be upon him) in mursal form, and it is also narrated from Abu Hurayrah (may Allah be pleased with him) as marfu'. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6730
It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him): "A man died who had done no good deed except three handfuls of earth that he had thrown into a grave, so all his sins were forgiven."
This is a good (hasan) mawquf report on this topic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6731
Umayr bin Sa'id said that Ali (may Allah be pleased with him) performed the funeral prayer over Yazid bin Mukaffif and said four takbirs in it, and then threw earth into his grave.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6732
Umayr bin Sa'id narrates that he saw Sayyiduna Ali (may Allah be pleased with him) throw two or three handfuls of earth into the grave of Ibn Mukaffif.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6733
Ali bin Zayd narrates that when Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) buried Sayyiduna Zayd bin Thabit (may Allah be pleased with him) and threw earth on his grave, he said: This is how knowledge is buried. I related this to Ali bin al-Husayn (may Allah have mercy on him), and he said: As for Sayyiduna Ibn Abbas (may Allah be pleased with them both), by Allah, he was remarkable; by Allah! A great deal of knowledge was buried with him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6734