Musannaf Ibn Abi Shayba 13:2254

Abu Bakr narrated to us, he said: Ibn Mubarak narrated to us, from Hakim ibn Ruzayq, from his father, from Sa’id ibn al-Musayyib, regarding a man who had a claim against another man for one thousand large bricks, and the large ones are sold for two hundred, and the small ones for two hundred and fifty. He said: He may reduce it from his right, for he is permitted to waive it if he wishes.