Muwatta Malik, Book 2, Hadith 68 (In-Book)

Yahya related to me from Malik from Nafi that Abdullah ibn Umar used two fingers to take water to his ears.

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَأْخُذُ الْمَاءَ بِأَصْبُعَيْهِ لأُذُنَيْهِ ‏.‏

sunnah.com

also referenced under: Book 2, Hadith 38 (USC-MSA)