Albert Barnes on Matthew 26:23

He that dippeth his hand with me in the dish. The Jews, at the observance of this ordinance, used a bitter sauce, made of bunches of raisins, mixed with vinegar and other seasoning of the like kind, which they said represented the clay which their fathers were compelled to use in Egypt, in making brick; thus reminding them of their bitter bondage there. This was probably the dish to which reference is made here. It is not improbable that Judas reclined near to our Saviour at the feast; and by his saying it was one that dipped with him in the dish, he meant one that was near to him, designating him more particularly than he had done before. John adds, (Jn 13:23-30); Jn 13:23 and following, that a disciple (i.e. John himself) was reclining on Jesus' bosom; that Simon Peter beckoned to him to ask Jesus more particularly who it was; that Jesus signified who it was, by giving Judas a sop; i.e., a piece of bread or meat, dipped in the thick sauce; and that Judas, having received it, went out to accomplish his wicked design of betraying him. Judas was not, therefore, present at the institution of the Lord's Supper.

(z) "He that" Ps 41:9, 55:12-15