Musannaf Ibn Abi Shayba 9:253

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Sa’id, from Qatadah, from Anas bin Malik and Sa’id bin al-Musayyib, that they both said: If he emancipates her for Allah the Exalted, he shall not return to it [i.e., take her back]. And they both saw no harm in him emancipating her in order to marry her.