Sahih Bukhari Volume 5, Book 57, Hadith Number 109.

Narated By Ibn Abi Mulaika : Somebody said to Ibn ‘Abbas, “Can you speak to the chief of the believers Muwaiya, as he does not pray except one Rak’a as Witr?” Ibn ‘Abbas replied, “He is a Faqih (i.e. a learned man who can give religious verdicts).”