Imam Ibn Hajar al-Asqalani (Allah have mercy on him) have said that: Imam bayhaqi have written a book over the life of Prophets (عليه السلام) in graves in that book he have written a hadith narrated by Hazrat Anas (رضي الله عنهم) that Prophets (عليه السلام) are alive in their graves and they pray namaz aswell. he have narrated this hadith on the way of Yah'ie bin Abi kathir and he is narrator of sahi hadiths. he have narrated from Mustalim bin Saeed and Imam Ahmad bin hanbal have declared him "Sound" narrator and Imam ibn Hibban have narrated this hadith from Hajaj Aswad and he is Ibn Abi Ziyad Basri and Imam Ahmad have declared him "Sound" narrator and Ibn Moeen have narrated this hadith from Hazrat Thabit and Imam Abu Abu Yala have also mentioned this hadith in his masnad on the same way and Imam Bazar have also declared it "Sound" and Imam Bayhaqi have also declared it "Sound" . [Fath al-Bari, Volume 006: Page No. 487]