Source of Shaykh Ahmad's knowledge

After noticing an interest in grammar on the part of his son, Shaykh Zayn al-Din (father of Shaykh Ahmad) sent him to a nearby village to study with a local scholar. Sometime during his studies there, young Ahmad began having visions and dreams in which a young man would teach him the meanings of Qur'anic verses, or he would visit strange worlds. Finally, he saw three of the twelve Shi'i Imams in a dream: the second Imam al-Hasan ibn Ali ibn Abi Talib, the fourth Imam Ali ibn al-Husayn ibn Ali, and the fifth Imam Muhammad ibn Ali ibn al-Husayn. The high point of this vision is when Imam al-Hasan places his mouth over that of Ahmad, who is lying flat on his back, letting him taste the Imam's saliva. Then the Imam places his hand on Ahmad's face, then his chest, sending a cool feeling through his heart. In the tradition of Shi'i mysticism, the receiving of the saliva of the Prophet or one of the Imams is symbolic of the transmission of some of their knowledge.

In the months that followed, young Ahmad began working on increasing his devotions and recitation of the Qur'an, perfecting his sincerity in those devotions, as well as deepening his meditations on world around him. The intensity of his visions increased until he reached a point where he could "visit" the Imams and the Prophet almost at will, and ask difficult questions of them. This continued, he says, throughout his studies and until his fame as a scholar and leader years later, when his visions of the Imams became intermittent. At one point he claims to have had a vision wherein the tenth Imam passed him twelve licenses, one from each Imam.

(Source : The Metaphysics and Cosmology of Process According to Shaykh Ahmad Ahsai by Idris Samawi Hamid, A dissertation submitted to the Department of Philosophy of State University of New York at Buffalo in partial fulfillment of the requirements for the degree of Doctor of Philosophy)

https://www.academia.edu/1436505/The_Metaphysics_and_Cosmology_of_Process_According_to_Shaykh_Ahmad_Al-Ahsāʾī_Critical_Edition_Translation_and_Analysis_of_Observations_in_Wisdom