Musannaf Ibn Abi Shayba 28:422

Waki’ narrated to us, from ‘Imran bin Hudayr, from Abu Mijlaz, who said: When al-Hurmuzan and al-Suran accepted Islam, ‘Umar said to them: "The jizya is only upon you [because you were not Muslims]. Indeed, Islam is truly enough to exempt one from the jizya."