1 Samuel 26:7

So David and Abishai came to the people by night: and, behold, Saul lay sleeping within the trench, and his spear stuck in the ground at his bolster: but Abner and the people lay round about him.

Cross-reference

In 1 Samuel 26:12, the deep sleep from the Lord explains why no one woke up - a divine enabling of David's mission.