April 24, 1 Samuel 30:7-15
David calls upon God for guidance, he asks Abiathar to come with the ephod, the symbol of the priest's office. Exactly what was done or how God answered is not told so I won't conjecture on this, it's important though that David realized he needed to go to God before taking any action.
There are a lot of things that we don't know about David's army, the age and physical condition of the men would be significant. They were on the march for three days to return home, when they got there it was a time of distress and sorrow and now another whole day of forced march to pursue their enemy. No doubt this takes a toll both physically and emotionally to the extent that a third of his forces can't continue. The discovery of the Egyptian left behind to die could be God's providence, giving David useful information.
There is a significant contrast between how David conducted raids and these Amalekites, when David raided he didn't take captives, it says he destroyed cities and killed everyone. Had his enemies shown the same level of brutality there would be no hope for recovering captives.