1766/1 - Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “It is better for anyone of you to sit on an ember and it burns his clothing and gets to his skin than to sit on a grave.” [Narrated by Muslim]
--
1) It is prohibited to sit on the graves of Muslims, for the inviolability of a Muslim is the same whether he is alive or dead.
2) It is recommended to give examples while preaching others, as this is one of the Prophet’s educational methods.