Sahih Bukhari
Companions of the Prophet
Volume: 005 / Book Number: 057 / Hadith Number: 110
Narrated Humran bin Abbas:
Muawiya said (to the people), "You offer a prayer which we, who were the companions of the Prophet never saw the Prophet offering, and he forbade its offering," i.e. the two Rakat after the compulsory 'Asr prayer.