1 Samuel 23:9
And David knew that Saul secretly practised mischief against him; and he said to Abiathar the priest, Bring hither the ephod. And David knew that Saul secretly practised mischief against him; and he said to Abiathar the priest, Bring hither the ephod.
At this point David and Abiathar were together as fugitives from Saul. Abiathar had escaped to David after Saul's slaughter of the priests. David had taken him in and pledged to protect him. The pledge rested on the fact that Saul was seeking the lives of them both.