Amr bin Shu'ayb narrates from his father, from his grandfather (Sayyiduna Abdullah bin Amr, may Allah be pleased with them both), that the Messenger of Allah (peace and blessings be upon him) said: "Whoever has been given a contract of manumission (mukatabah) for one thousand uqiyahs and pays all of it except ten uqiyahs, he is still a slave; and whoever has been given a contract for one hundred dinars and pays all of it, but ten dinars remain, he is still a slave."
(b) In the narration of Amr bin Asim and Abu al-Walid it is: "The slave who has been given a contract for one hundred dinars and pays all of it, with only ten dinars remaining due from him, will remain a slave; and the slave who has been given a contract for one hundred uqiyahs, with only ten uqiyahs remaining, will remain a slave."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21636