Musnad Ahmad 648:19

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from al-Hakam, who said: I heard Abu Wa'il say: When Ali sent Ammar and al-Hasan to Kufa to mobilize them, Ammar delivered a sermon and said: "I truly know that she is his wife in this world and the Hereafter, but Allah, the Almighty and Majestic, has tested you to see whether you will follow him or her."