Luke 2:50
"And they understood not the saying which he spake unto them."
Cross References (ranked by relevance)
Luke 18:34
And they understood none of these things: and this saying was hid from them, neither knew they the things which were spoken.
Luke 9:45
But they understood not this saying, and it was hid from them, that they perceived it not: and they feared to ask him of that saying.
Mark 9:32
But they understood not that saying, and were afraid to ask him.