Al-Matalib al-'Aliyah 823 — Burial

It is narrated from one of the Companions (may Allah be pleased with him) of the Prophet (peace and blessings be upon him) that the Prophet (peace and blessings be upon him) came to us at the time of a deceased person's burial and said: "Do not weigh down this companion of yours." Imam Sufyan bin Uyaynah (may Allah have mercy on him), explaining its meaning, said that it means the grave should not be made heavy by putting on it more earth than came out of its own pit; and sometimes the words of the hadith are narrated thus: "Lighten the burden of your companion." Imam Sufyan said that this too means not adding to the earth of the grave.
Imam Ibn Abi Umar recorded this narration in his Musnad; there is weakness in its chain because of an unnamed narrator; however, the command not to raise the grave high with earth is established by other sahih hadith.