Genesis 44:10

And he said, According to your words let it be. With whomsoever it is found he shall be my slave, but you shall be innocent.

ALSO NOW IT WERE RIGHT TO BE ACCORDING TO YOUR WORDS. “Indeed, this is only right. Verily it should be according to your words since you are all guilty in this matter. When there are ten men and a stolen thing is found in the possession of one of them, all of them are arrested. I, however, will deal with you inside the bounds [of justice, that is, I will deal with you more leniently]. He with whom it shall be found, he alone shall be my servant.” Thus the language of Rashi.
But according to this interpretation, the words, gam atah (also now), do not fit in well. (a true decision), how can the words gam atah (also now) fit into the context since these words suggest that now a new law is established. (Aboab.) See also my Hebrew commentary, p. 238. Perhaps Rashi is saying: “Also now, when according to your words, it is the law [that all be held guilty in the matter], he with whom it shall be found shall be my servant.” (also now) apply since this is a principle newly set forth. But this can hardly be correct since Joseph said, Far be it from me to do so. This shows that it is not the law that they all be held responsible for the theft. It is for this reason that he said: “Far be it from me, for I am the judge of the whole land, and far be it from me to do you wrong,” for all ten men are not guilty if a stolen article is found in the possession of one of them unless they all planned the theft and were united in going to steal it. Then, if one of them took it with the knowledge of all, they are all liable.
The correct interpretation would seem to be that at first he accused them all: Why have you repaid evil for good? You have done evil in so doing. And they freed themselves of the accusation by saying, “With whomsoever of thy servants it be found, let him die, since he is the thief, and we also, who are guiltless of the theft, will be my lord’s servants. Thus their opinion was that the thief, in whose possession it might be found, was the only one with knowledge of the theft, for if they were all involved in the theft, why should that one alone be put to death while the rest remain alive. In that case, all of them should be put to death or all of them should become servants, for they all bear equal legal responsibility. Rather, they pleaded that the others had no knowledge of the theft. They agreed that they should become servants as a …

כדבריכם כן הוא, you are truly all partners in all that you do. It is the custom of merchants to always attribute blame to one another. But I am not willing to go along; only the one in whose bag the goblet was found הוא יהיה לי עבד, he alone will be my slave.

גם עתה כדבריכם כן הוא. Even though now, in this instance the argument you cite is logical, correct, but in this special circumstance, the goblet in question belonging to the king, a man who has treated you well by giving back all your money in your sacks, the fact is that האיש אש אתו ימצא הגביע הוא יהיה לי עבד, and not all of you. Even this individual will not be sentenced to death as would be required if we applied the law in all its strictness.

ואתם תהיו נקיים. You will both be free from becoming slaves or any other form of punishment.

ויאמר, גם עתה כדבריכם כן הוא, he meant that although legally speaking the law is as you say, I will be more lenient with you, etc.

אשר ימצא, the one in whose possession, etc. Other commentators interpret the words כדבריכם כן הוא to mean that your argument that you are honest as proven by your bringing back the money you found is acceptable, [but it does not apply to either Shimon or Binyamin, neither of whom have brought back any money.] but if the goblet is found in someone’s sack, that individual will have to be my master’s slave. I will however, not hold you responsible by association.

'גם עתה כדבריכם כן הוא וגו, “also now I accept what you have said;” this appears very difficult, as the brothers had suggested that the thief if found among them should be given the death penalty, whereas they as relatives of the thief would become slaves were prepared to become slaves. Joseph’s messenger had only been concerned with punishing the thief himself, and even at that not to execute him. We must therefore interpret the messenger’s words as meaning that he accepted the brothers’ suggested punishment for themselves, if and when one of them were to be found guilty. Joseph’s messenger said that he would be more generous with them than they would be with themselves if it turned out that they were not guilty. An alternate interpretation of the line quoted: “I accept what you said concerning that you had already proved your innocence, and that you are not thieves. However, this applies only to nine of you. Neither Binyamin nor Shimon had brought back any money.” Binyamin had not been in Egypt, ad Shimon had not returned to the land of Canaan, having been in jail during your absence. He must therefore search the sacks of these two.

יהיה לי עבד, “shall be a slave for me.” This is very strange, as the man saying these words was only a servant of Joseph himself. He should have said: “will be a servant to my master.” Perhaps we can understand this wording as the servant (messenger) said that seeing he is the messenger, he is responsible to his master for anything that he has not carried out correctly in his mission. Therefore, in the first instance, the brothers are his responsibility to deal with. Legally, therefore, the guilty brother becomes his slave initially.