C. F. Keil and Franz Delitzsch on 1 Samuel 20:6

1Sa 20:6 “If thy father should miss me, then say, David hath asked permission of me to hasten to Bethlehem, his native town; for there is a yearly sacrifice for the whole family there.” This ground of excuse shows that families and households were accustomed to keep united sacrificial feasts once a year. According to the law in Deu 12:5., they ought to have been kept at the tabernacle; but at this time, when the central sanctuary had fallen into disuse, they were held in different places, wherever there were altars of Jehovah - as, for example, at Bethlehem (cf. 1Sa 16:2.). We see from these words that David did not look upon prevarication as a sin.