كتاب الأيمان
27  
The Book of Oaths
(12)
Chapter: One who frees his share in a slave
(12)
باب مَنْ أَعْتَقَ شِرْكًا لَهُ فِي عَبْدٍ ‏‏
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 ‏"‏ ‏.‏
Reference : Sahih Muslim 1503d
In-book reference : Book 27, Hadith 79
USC-MSA web (English) reference : Book 15, Hadith 4109
  (deprecated numbering scheme)