Musnad Ahmad 1153:1126

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from al-Ash'ath ibn Sulaym, from his father, from Masruq, from 'Aishah, that she said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to love the right side in all of his affairs." Then al-Ash'ath said at the end: "He used to love the right side as much as he was able in his combing, his footwear, and his purification."