It is narrated from Sayyiduna Ibn Amr, may Allah be pleased with him, that once I submitted in the presence of the Messenger, "O Messenger of Allah! Should I write down the things I hear from you?" The Noble Prophet, peace and blessings be upon him, said: "Yes." I asked, "In both states of your pleasure and displeasure?" The Noble Prophet, peace and blessings be upon him, said: "Yes, because nothing comes out of my tongue except the truth."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6930