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 1501 d

Ibn 'Umar reported Allah's Messenger (ﷺ) as saying:

He who emancipates his share in the slave, it is his responsibility to secure full freedom for him provided he (the slave) has enough money to pay the (remaining) price, but it he has not so much money he would be emancipated to the extent that the first man emancipated.
حَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ أَعْتَقَ شِرْكًا لَهُ مِنْ مَمْلُوكٍ فَعَلَيْهِ عِتْقُهُ كُلُّهُ إِنْ كَانَ لَهُ مَالٌ يَبْلُغُ ثَمَنَهُ فَإِنْ لَمْ يَكُنْ لَهُ مَالٌ عَتَقَ مِنْهُ مَا عَتَقَ ‏"‏ ‏.‏
Reference : Sahih Muslim 1501d
In-book reference : Book 27, Hadith 73
USC-MSA web (English) reference : Book 15, Hadith 4103
  (deprecated numbering scheme)