After the story of Avimelech and how he took Sarah as a wife without realizing that she was a married woman, the Torah tells us that Avrohom Avinu davened for Avimelech. Chaza”l say that since Avimelech was afflicted with a sickness as a result of Avrohom Avinu’s statement that Sarah was in fact his sister, Avrohom was responsible to make sure that he got healed.
Rabbi Aharon Dovid Singer
Rosh Kollel, NMB Kollel