Sayyidah Aishah (may Allah be pleased with her) says that the Prophet (peace and blessings be upon him) heard the loud voices of disputants at the door. When the one asked the other to reduce the price and to be lenient, he would say: By Allah! I will not do it.
The Prophet (peace and blessings be upon him) went out to them and asked: "Where is the one who swears that he will not do good?" He said: O Messenger of Allah! It is I. He said: Whatever he prefers is his.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10626