It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Keep these bodies pure, may Allah purify you. There is no servant who spends the night in a state of purity except that an angel spends the night with him in his garment; whenever he turns over at any hour of the night, the angel says: 'O Allah, forgive Your servant, just as he spent the night in a state of purity.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13564