Musannaf Ibn Abi Shayba 27:382

Abu Usama narrated to us, he said: As-Salt ibn Bahram informed us, from Sayyar Abu al-Hakam, that when Abu Bakr became ill, he looked out his head to the people from a small window and said: "O people, I have made a covenant; are you satisfied with it?" The people stood up and said: "We are satisfied." Then Ali stood up and said: "We will not be satisfied unless it is Umar ibn al-Khattab." And so it was Umar.