Musnad Ahmad 1153:624

'Affan narrated to us, Sakhr ibn Juwayriyah narrated to us, he said: Isma'il al-Makki narrated to us, he said: Abu Khalaf, the freed slave of Banu Jumah, narrated to me that he entered with 'Ubayd ibn 'Umayr upon 'A'ishah, the Mother of the Believers, in the portico of Zamzam; there was no shade in the mosque other than it. She said: "Welcome and greetings to Abu 'Asim," meaning 'Ubayd ibn 'Umayr. "What prevents you from visiting us or dropping by?" He said: "I fear that I might become a burden." She said: "You would not do that." He said: "I came to ask you about a verse in the Book of Allah, the Mighty and Majestic: how did the Messenger of Allah, peace and blessings of Allah be upon him, recite it?" She said: "Which verse?" He said: "'Those who give what they give' (alladhina yu'tuna ma atau), or 'Those who do what they have done' (alladhina ya'tuna ma atau)?" She said: "Which of the two is more beloved to you?" He said: "I said: By the One in Whose hand is my soul, one of them is more beloved to me than the entire world, or the world and what is in it." She said: "Which of them?" I said: "'Those who do what they have done' (alladhina ya'tuna ma atau)." She said: "I bear witness that the Messenger of Allah, peace and blessings of Allah be upon him, used to recite it that way, and that is how it was revealed." Or she said: "I bear witness that it was revealed that way, and the Messenger of Allah, peace and blessings of Allah be upon him, used to recite it that way, but the spelling is a letter [different]."