Musannaf Ibn Abi Shayba 34:206

Ahmad ibn Abd al-Malik ibn Waqid narrated to us, Zuhayr narrated to us, Abu Ishaq narrated to us, he said: It was said to Qutham, "How did Ali inherit from the Prophet, may Allah bless him and grant him peace, to the exclusion of you?" He said, "By Allah, he was the first of us to join him and the closest of us to him."