Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: I poured water for ablution for the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "O Allah, grant him understanding of the religion and teach him interpretation (ta'wil, the exegesis of the Qur'an)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11158