97 - Chapter: Building over Graves

2028 - Yusuf ibn Sa'id informed us, saying: Hajjaj narrated to us, from Ibn Jurayj, who said: Abu al-Zubayr informed me that he heard Jabir say: The Messenger of Allah, peace and blessings be upon him, forbade plastering graves, or building over them, or anyone sitting upon them.(1)

98 - Chapter: Plastering Graves with Gypsum

2029 - 'Imran ibn Musa informed us, saying: 'Abd al-Warith narrated to us, saying: Ayyub narrated to us, from Abu al-Zubayr

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And it was also recorded by Ahmad (14149) from Muhammad ibn Bakr al-Barsani, from Ibn Jurayj, from Sulayman ibn Musa alone, with it, without his statement: "or adding to it."
It will also appear in the following narration — without mention of the two phrases and with the addition of the prohibition of sitting on graves — via the route of Hajjaj, from Ibn Jurayj, and in narration (2029) — abbreviated to the prohibition of plastering graves with gypsum — via the route of Ayyub, both from Abu al-Zubayr alone, with it.

(1) Its chain of transmission is sound. Ibn Jurayj — who is 'Abd al-Malik ibn 'Abd al-'Aziz — and Abu al-Zubayr — who is Muhammad ibn Muslim ibn Tadrus — both explicitly stated that they heard it directly, thus removing any suspicion of tadlis (concealment) on their part. Hajjaj is Ibn Muhammad al-Misisi al-A'war. It is in "Al-Sunan al-Kubra" under number (2166).
It was also recorded by Ahmad (14647), Muslim (970): (94), and Ibn Hibban (3165) via the route of Hajjaj ibn Muhammad, with this chain of transmission.
See also what precedes and follows it.

His statement: "plastering graves" (taqsis al-qubur) means coating them with gypsum. "Or building over them" — this is the conjunction of a verb with a verbal noun, with "an" (that) implied. "Or anyone sitting upon them" — it is said: he meant sitting to relieve oneself, or sitting in mourning and grief by remaining at the grave and not leaving it, or he meant showing respect for the deceased and magnifying the matter, such that sitting upon it would be an act of disregard for the deceased and for death. These are various opinions.