Maliks Muwatta Book 3, Hadith Number 73.
Section : Looking in the Prayer at What Distracts You from It.
Malik related to me from Hisham ibn Urwa from his father that the Messenger of Allah, may Allah bless him and grant him peace, wore a fine striped garment from Syria, and then gave it to Abu Jahm and took a plain, rough, garment in return. Abu Jahm asked, “Messenger of Allah! Why?” He said, “I looked at its stripes in the prayer.”