Maliks Muwatta Book 31, Hadith Number 83.

Yahya related to me from Malik from Uthman ibn Hafs ibn Khalda from Ibn Shihab from Salim ibn Abdullah that Abdullah ibn Umar was asked about a man who took a loan from another man for a set term. The creditor reduced the debt, and the man paid it immediately Abdullah ibn Umar disliked that, and forbade it.