Encyclopedia of Prophetic Hadiths

"When any of you sleeps, the devil ties three knots at the back of his head, striking each knot: Ahead of you is a long night, so keep sleeping. When he wakes up and remembers Allah, one knot is undone; when he performs ablution, one knot is undone; and when he prays, one knot is undone, and he gets up in the morning active and in good spirits; otherwise, he gets up in the morning low-spirited and sluggish."

The Prophet (may Allah’s peace and blessings be upon him) used to perform ablution upon every prayer. I asked: "What did you guys use to do?" He said: "Ablution would remain valid for any of us until he broke it."