Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that he used to say, regarding a person who makes a contract of manumission with his slave for gold and silver payable in installments, that he disliked that he should say: Give me such-and-such quickly, and whatever remains is yours.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21711