Mark 14:40
And when he returned, he found them asleep again, (for their eyes were heavy,) neither wist they what to answer him.
Cross-references
Mark 14:37
Parallel
Mark 14:37 immediately follows — Jesus confronts Peter for sleeping, directly connected to the same moment.
Mark 13:36
Prophetic fulfillment
In Mark 13:36, Jesus warned about being found sleeping — here that warning is realized as he finds them asleep.
Luke 22:45
Parallel
Luke 22:45 adds detail that they were sleeping from sorrow — the same Gethsemane event as Mark 14:40.