Musnad Ahmad 1153:1540

'Abd al-Malik ibn 'Amr Abu 'Amir narrated to us, he said: Hisham narrated to us, from Yahya, from Abu Salamah, that 'Aishah narrated to him that the Prophet, peace and blessings of Allah be upon him, "did not use to fast in any month of the year more than his fasting in Sha'ban, for he used to fast all of Sha'ban." And he used to say: "Take upon yourselves of the deeds what you can bear, for Allah, the Almighty and Majestic, does not grow weary until you grow weary." And indeed, "the most beloved of prayer to the Messenger of Allah, peace and blessings of Allah be upon him, was that which was performed consistently, and when he performed a prayer, he would perform it consistently."