Somebody said to Ibn `Abbas, "Can you speak to the chief of the believers Mu`awiyah, 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) ."
Sahih al-Bukhari Book 62, Hadith 110
← Previous Hadith Muawiya offered one rak`a witr prayer after the `Isha prayer, and at that time a freed slave of Ibn `Abbas was present. He (i.e. the slave) went to Ibn `Abbas (and told him that Muawiya offered one rak`a witr prayer). Ibn `Abbas said, "Leave him, for he was in the company of Allah's Messenger (ﷺ)."

Sahih al-Bukhari Book 62, Hadith 109 Next Hadith → Muawiya said (to the people), "You offer a prayer which we, who were the companions of the Prophet (ﷺ) never saw the Prophet (ﷺ) offering, and he forbade its offering," i.e. the two rak`at after the compulsory `Asr prayer.

Sahih al-Bukhari Book 62, Hadith 111