I saw the Messenger of Allah ﷺ, when he performed ablution, work his little finger between the toes of his feet.
حدثنا موسى بن داود قال أخبرنا ابن لهيعة عن يزيد بن عمرو عن أبي عبد الرحمن الحبلى
رأيت رسول الله ﷺ إذا توضأ خلل أصابع رجليه بخنصره
Its chain of transmission is hasan because of Ibn Lahia. Abu Dawud narrated the hadith in 1/37, no. 148, in the chapter on purification, washing the feet, Tirmidhi in 1/56, no. 38, where he said it is hasan sahih, and Darimi in 1/191, no. 705.