Ibn 'Abbas reported that Allah's Messenger (ﷺ) came to privy and I placed for him water for ablution, When he came out he said: Who placed it here? And in a version of Zuhair they (the Companions) said, and in the version of Abu Bakr (RA) (the words are): I said: It is Ibn 'Abbas (who has done that), whereupon he (the Holy Prophet) said: May Allah grant him deep understanding of religion.
Explanation & Benefits
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Benefits and Issues: The Messenger of Allah (sallallahu alayhi wa sallam), on various occasions, being pleased with the intelligence and acumen of Ibn Abbas (radi Allahu anhu), supplicated for him with different appropriate words. Sometimes he said: "O Allah, grant him understanding of the religion," or "O Allah, teach him the Book," or "Teach him wisdom." At other times he said, "O Allah, grant him understanding of the religion and teach him interpretation," or "Teach him wisdom and the interpretation of the Book." On this basis, he was given the title "Interpreter of the Qur'an."
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 6368