"I saw the Messenger of Allah performing ablution, and he ran his little finger between his toes." (Sahih)

Another chain with similar wording.
Sunan Ibn Majah Book 1, Hadith 180
← Previous Hadith "The Messenger of Allah said: 'The ears are part of the head.'"

Sunan Ibn Majah Book 1, Hadith 179 Next Hadith → 'The Messenger of Allah said: 'When you get up for prayer, perform ablution properly and make the water run between your toes and your fingers.'"

Sunan Ibn Majah Book 1, Hadith 181