The Messenger of Allah ﷺ said, "The prophets are alive in their graves, praying."
قال رسول الله ﷺ: الأنبياء أحياء في قبورهم يصلون.
Abu Yaala related it in his Musnad (3425) from Abu Jahm Azraq bin Ali, who said, Yahya bin Abu Bukayr narrated to us, Mustalim bin Saeed narrated to us, from Hajjaj, from Thabit, from Anas bin Malik, and he mentioned it. Bayhaqi extracted it through the route of Abu Yaala in Hayat Al-Anbiya (p. 72). As for Azraq, who is Abu Jahm Hanafi, Azraq bin Ali, Hafiz said of him, "Truthful, but he transmits rare, unusual reports." I say, however he was not the sole narrator of it, for Hasan bin Arafah also narrated it, saying, Hasan bin Qutayba Madaini narrated to me, Mustalim bin Saeed narrated to us, with his chain, in like manner.Bayhaqi related it through his route in Hayat Al-Anbiya (p. 70) and said, "This is counted among the unique reports of Hasan bin Qutayba Madaini." He said this despite having related it through the route of Abu Jahm Azraq bin Ali, as mentioned before, and through other routes as well, even though some of them contain a narrator who is suspect.The hadith has another route, which Abu Naeem extracted in Akhbar Isbahan (2/82) through the route of Abdullah bin Ibrahim bin Sabbah, from Abdullah bin Muhammad bin Yahya bin Abu Bukayr, who said, Yahya bin Abu Bukayr narrated to us with his chain, in like manner.From these corroborating narrations it becomes clear that Azraq bin Ali did not transmit anything unusual in this report, and likewise that Hasan bin Qutayba Madaini was not its sole narrator. As for the "life" mentioned here, it is a life in the intermediate realm (barzakh), and has nothing whatsoever to do with worldly life. For more on this, see the book Al-Iman bil-Anbiya alayhim as-salam.