MN 79 Culasakuladayin: The Shorter Discourse to Sakuludayin
The Buddha asks Sakuludayin what his teacher’s teaching is. He replies “this is the perfect splendour”. The Buddha asks “what is that splendour?” but gets a repetition in reply.
The Buddha takes apart the teaching by giving a simile:
Suppose someone said ‘I am in love with the most beautiful girl in the country’ and people might ask him ‘What class is she from? What is her name? Where is she from? Is she tall or short?’ if he would not be able to answer those questions they would say ‘So you are in love with a girl you have never known or seen’. His talk would amount to nonsense.