Barnes
All the circumstances, also, lead us to suppose that he observed it at the usual time and manner,
Mat_26:17,
Mat_26:19. The only passage which has led to a contrary opinion is this in John; but here the word passover does not, of necessity, mean the paschal lamb. It probably refers to the Feast which followed the sacrifice of the lamb, and which continued seven days. Compare
Num_28:16-17. The whole feast was called the Passover, and they were unwilling to defile themselves, even though the paschal lamb had been killed, because it would disqualify them for participating in the remainder of the ceremonies (Lightfoot).