الكافي 1/2/21/3

3. Ali ibn Ibrahim has narrated from his father from ibn abu Najran from ‘Asim ibn Humayd from Mansur ibn Hazim who has said the following. “I said to (Imam) abu ‘Abdallah عليه السلام , ‘It is confuses me that when I ask you a question and you give an answer and then other person comes and you give a different answer for the same question.’” The Imam replied, “We answer people in a larger and reduced forms.” I then asked, “Did the Sahabah, companions of the holy Prophet speak the truth or lies when narrating his Hadith?” The Imam replied, “They spoke the truth.” I then said, “Why then they have differences?” Have you not considered the fact that a man would come to the holy Prophet صلى الله عليه وعلى آله وسلم and ask a question and would give him an answer and then he would answer that would abrogate the previous answer. Thus, Ahadith abrogated other Ahadith.”