The Messenger of Allah sallAllahu 'alayhi wa sallam said: “The grave is the first of the stages of the Hereafter; whoever is saved from it, whatever comes afterwards will be easier for him, but if he is not saved from it, what comes afterwards will be worse for him”.

He (sallAllahu 'alayhi wa sallam) also said, “I have never seen any scene but the grave is more frightening than it.”

 
[Tirmidhi, 2308, Hasan by Albani and Ibn Maajah 4267, Hasan by Zubair Ali Zai.]