Mishkat al-Masabih 3395
Jabir said:
In the time of God’s Messenger and of Abu Bakr we sold slave women who had borne children, but when ‘Umar was in power he forbade us to do so and we stopped. 

Abu Dawud transmitted it.
وَعَنْ جَابِرٍ قَالَ: بِعْنَا أُمَّهَاتِ الْأَوْلَادِ عَلَى عَهْدِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَأَبِي بَكْرٍ فَلَمَّا كَانَ عُمَرُ نَهَانَا عَنْهُ فَانْتَهَيْنَا. رَوَاهُ أَبُو دَاوُد