Ja'far bin Muhammad (may Allah have mercy on him) narrates from his father that water was sprinkled on the grave of the Prophet (peace and blessings be upon him), pebbles were placed on it, and the grave was raised to the height of a hand-span.
This is mursal (the Companion is missing from the chain). Al-Waqidi narrated it with a chain of his own from Jabir, and that is rejected.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6737