Shabat 108a: This could be the beginning of a beautiful relationship...

Rav and Shmuel are two of the most famous sages of the Gemara.  The Talmud is full of their disputes.  Below is the story of how they met.

Shmuel and Karna (a friend of his) were sitting by the bank of the Malka river.  They saw the water was cloudy and full of waves.  Shmuel said to Karna, 'There is a great man coming from Eretz Israel.  He is in digestive distress, and the waves are rising up to meet him.  Go and test his knowledge.'

[Karna finds this great man, Rav, and asks him some questions about biblical exegesis.  After his last question, Karna asks for a clarification that betrays the fact that Karna himself is knowledgeable, and was testing Rav.]  Rav asked Karna, 'What is your name?'  Karna said, 'Karna.'  Rav said, 'May it be [G-d's] will that there be a thorn [which sounds like 'Karna'] in your eye.'  [Our sages explain that Rav was mad because he was tricked into being tested.]  Finally, Shmuel invited Rav into his home and fed him barley bread, fish mash, and beer, but didn't tell Rav  where the bathroom was, in order that Rav's insides should be purged [of the source of digestive distress.  Shmuel was a doctor. ]  Rav [not knowing that this was meant to cure him], cursed and said, 'Whoever caused me this distress will not be survived by his own sons.'  And so it came to pass.