John Gill Commentary 1 Samuel 20:26

"Nevertheless Saul spake not anything that day: for he thought, Something hath befallen him, he is not clean; surely he is not clean." — 1 Samuel 20:26 (ASV)

Nevertheless, Saul spoke not anything that day About David's absence, took no notice of it, said nothing about it:

for he thought something had befallen him ; some impurity, some nocturnal pollution, see (Leviticus 15:16) ;

he [is] not clean, surely he [is] not clean ; which he repeated in his mind for the confirmation of it, and in contempt, and to the reproach of David; and in this way he accounted for his absence the first day, and so was easy, it not being lawful and fitting for an unclean person in a ceremonial sense to eat of the peace offerings, which Saul and his family were now partaking of.