Musnad Ahmad 28:404

Ya'qub narrated to us, my father narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn Ibrahim ibn al-Harith, from Abu Salamah ibn 'Abd al-Rahman ibn 'Awf, who said: I entered upon 'Abd Allah ibn 'Amr ibn al-'As in his house, and he asked me, while he thought that I was from the sons of Umm Kulthum bint 'Uqbah. I said to him: "I am only of the Kalbiyyah, the daughter of al-Asbagh, and I have come to you to ask you about what the Messenger of Allah, peace and blessings of Allah be upon him, entrusted to you or said to you?" He said: "I used to say during the time of the Messenger of Allah, peace and blessings of Allah be upon him: 'I will surely recite the Quran every day and night, and I will surely fast for my entire life.' That reached the Messenger of Allah, peace and blessings of Allah be upon him, regarding me, so he came to me and entered my house and said: 'Has it not reached me, O 'Abd Allah, that you say: I will surely fast for my entire life, and I will surely recite the Quran every day and night?'" He said: "I said: 'Yes, I have said that, O Prophet of Allah.' He said: 'Do not do that. Fast three days of every month.' I said: 'I am stronger than that.' He said: 'Then fast on Monday and Thursday.' I said: 'I am stronger than that, O Prophet of Allah.' He said: 'Then fast one day and break your fast one day, for that is the most balanced fasting before Allah, and it is the fasting of Dawud, peace be upon him. And he would not break his promise when he promised, and he would not flee when he encountered [the enemy]. And recite the Quran once every month.'" He said: "I said: 'I am stronger than that, O Prophet of Allah.' He said: 'Then recite it once every half month.' I said: 'I am stronger than that, O Prophet of Allah.' He said: 'Then recite it every seven [days], and do not exceed that.'" Then the Messenger of Allah, peace and blessings of Allah be upon him, departed.