Musnad Ahmad 1153:1199

'Uthman ibn 'Umar narrated to us, Ibn Abi Dhi'b informed us, from al-Zuhri, from Yahya ibn Sa'id ibn al-'As, from his father, from 'Aishah, that Abu Bakr sought permission to enter upon the Messenger of Allah, may Allah bless him and grant him peace, while the Messenger of Allah, may Allah bless him and grant him peace, was wearing a *mirt* (a garment). He then mentioned its meaning.