Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: Once the Prophet (peace and blessings be upon him) was going around a date-palm orchard in Madinah. The people began to say: Its yield will be one wasq. The Prophet (peace and blessings be upon him) said: Its yield will be such and such. The people said: Allah and His Messenger have spoken the truth. Then the Prophet (peace and blessings be upon him) said: I am a human being like you. Whatever I tell you from Allah Almighty is the truth, and whatever I say from myself, then I am a human being: I may give a correct opinion and I may also err.
Al-Bazzar recorded it, and its chain is hasan (good), except for al-Bazzar's teacher Isma'il bin Abdullah al-Asbahani, for I have not seen anyone who has written a biography of him.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 837