Sahih Muslim 1503 d
This hadith has been narrated on the authority of Shu'ba with the same chain of transmitters (and the words are):
" He who emancipates a portion in a slave, he should (secure full) freedom for him from his property."
وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، بِهَذَا الإِسْنَادِ قَالَ ‏
"‏ مَنْ أَعْتَقَ شَقِيصًا مِنْ مَمْلُوكٍ فَهُوَ حُرٌّ مِنْ مَالِهِ ‏"‏ ‏.‏