Sunan Ibn Majah Book 1, Hadith 180

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

Another chain with similar wording.

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