Majma al-Zawaid — Hadith 525

A man from (the tribe of) Abs relates: Once I was walking with Sulayman along the bank of the river Tigris. He said: "O man from Banu Abs! Go down and drink!" So I drank. Then he said: "Drink (more)!" So I drank. He asked: "How much has the water you drank decreased the Tigris?" I replied: "It has not decreased it at all." He said: "Knowledge is like that too; however much is taken from it, it does not decrease." After this the narrator mentioned the whole narration, which will come later in full in the chapter on asceticism (zuhd), in the chapter on the way of life of the predecessors (salaf).
Tabarani recorded it in al-Mu'jam al-Kabir, and its chain contains a narrator who is not named.