الكافي 1/2/2/1

1. Muhammad b. al-Hasan has narrated from Ali b. Muhammad from Sahl b. Ziyad from Muhammad b. ‘Isa from Ubaydullah al-Dihqan from Durust al-Wasiti from Ibrahim b. Abdul Hamid from Abul Hasan Musa عليه السلام who has said: “Once Rasulullah صلى الله عليه وعلى آله وسلم entered the Mosque and found a group of people gathered around a man. He asked, 'Who is he?'. It was said that he was a Allamah. He then asked them, 'What is that?'. They replied that he is the most learned man about the genealogy, the chronology, and the history of the pre-Islamic days of darkness and the poetry of Arabs. He عليه السلام said, so the Prophet صلى الله عليه وعلى آله وسلم then stated that ‘such knowledge doesn't harm the one who is ignorant of it or benefit the one who knows it.' Then he صلى الله عليه وعلى آله وسلم added: ‘Knowledge consists of three kinds: A clear verse (of the Qur'an), a just obligation (i.e. a legal ruling) or an established sunnah (i.e. a hadith). Anything else is of the extra achievements.”’