Al-Matalib al-'Aliyah 3067 — The vastness of knowledge

It is narrated from a man of Banu Abs that he said: I was with Sayyiduna Salman al-Farisi (may Allah be pleased with him), and when we passed by the river Tigris he said: "O brother of Banu Abs, dismount and drink." So I dismounted and drank. Then he said again: "Dismount and drink." So I dismounted again and drank. After that he asked me: "O brother of Banu Abs, what has your drinking taken away from the water of the Tigris?" I said: "What could my drinking possibly take away from the water of the Tigris?" He said: "Knowledge is exactly like this; it never runs out, so be sure to take from it what can benefit you."
Abu Ya'la recorded it in his Musnad; one narrator in its chain is unnamed, but its meaning is established by other authentic hadith and reports.