Sayyiduna Ibn Umar (may Allah be pleased with them both) said: I heard the Prophet (peace and blessings be upon him) say: "On the day a man was placed in his grave, two angels came to him and said to him: We are going to strike you a blow. He said to them: For what will you strike me? They struck him such a blow that his grave was filled with fire from it. Then they left him until he regained consciousness and his terror left him, and he said to them: For what did you strike me? They said: You prayed a prayer without purification, and you passed by a man who was being wronged and did not help him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13553