Musnad Ahmad 30:323

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "At the nape of the head of one of you is a rope in which are three knots. If he wakes up and remembers Allah, a knot is untied. If he gets up and performs ablution, a knot is untied. If he gets up for prayer, all his knots are untied." He said: "So he wakes up energetic and in good spirits, having attained goodness. But if he does not do so, he wakes up lazy and in bad spirits, having attained no goodness."