It is narrated from Sayyiduna Ibn Amr (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: "If a slave has agreed to gain freedom by paying one hundred uqiyah as the price of his contract and he pays ninety uqiyah, he will still remain a slave (until he completes the full payment). Similarly, if a slave contracts for one hundred dinars and pays all except ten dinars, he will still remain a slave."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6726