John 11:13 KJV

Howbeit Jesus spake of his death: but they thought that he had spoken of taking of rest in sleep.
John 11:13, King James Version

In context

12 Then said his disciples, Lord, if he sleep, he shall do well.

13 Howbeit Jesus spake of his death: but they thought that he had spoken of taking of rest in sleep.

14 Then said Jesus unto them plainly, Lazarus is dead.