Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Dawood bin Kurdus that Hazrat Umar Farooq made a peace agreement with the Christians of Banu Taghlib on the condition that double the amount of zakat would be taken from them. And their children would not be made Christians, nor would they be forced into any other religion. Dawood, the narrator, says that there is no guarantee for them; indeed, they became Christians.