It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "There is no human being but that in his head there is a bridle held in the hand of an angel. When he is humble, it is said to the angel: 'Raise his bridle' (that is, raise him up); and when he is arrogant, it is said to the angel: 'Lower his bridle.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12883