Musannaf Ibn Abi Shayba 28:453

Affan narrated to us, he said: Abd al-Wahid narrated to us, he said: Abu Bakr narrated to us, he said: Abu Hanzala bin Nu'aym wrote that Sa'd wrote to Umar: "We have taken land whose people did not fight us." He said: So Umar wrote to him: "If you wish to divide it among yourselves, then divide it. And if you wish to leave it so that its people may cultivate it, and whoever enters among you afterward shall have a share in it, then do so. For I fear that you will dispute over it and over its irrigation, and thus some of you will kill others." So Sa'd wrote to him that the Muslims have agreed that their opinion follows your opinion. So he wrote to him that they should return the slave-women to a woman who became pregnant by a man from the Muslims.