Tafsir of Ad-Dhariyat 51:25

(When they entered upon him): This is an adverbial phrase for the [implied] discourse, as it is an adjective in its original sense; or for the guests; or it is linked to (honored) if what is intended is the honoring of Abraham, for the honor bestowed upon them by Allah, the Exalted, is not restricted to a specific time. Alternatively, it is in the accusative case due to an implied "remember."

They said, "Peace": That is, "We greet you with peace." In Al-Bahr, it is stated that the verb is omitted because the verbal noun (masdar) occupies its place; thus, it belongs to the class of verbal nouns whose verbs must be omitted. Ibn ‘Atiyyah said: It is possible to interpret "Peace" (salaman) as having the meaning of "a statement," such that the meaning would be: "They said a greeting and a statement." It is also attributed to Mujahid that the meaning is "peace," though this is not strong.

He said, "Peace": Meaning, "Upon you is peace." He shifted it to the nominative case (using the noun form) to denote permanence, so that his greeting would be better than theirs, as an act of superior etiquette and honoring. It is also said that "Peace" (salam) is the predicate of an omitted subject, meaning, "My state is peace." Both were also recited in the nominative case. It was also recited as silaman (with a kasrah on the sin and a sukūn on the lam), with the accusative case, where silm is equivalent to salam. Ibn Waththab, al-Nakha'i, Ibn Jubayr, and Talha recited it as silaman, while others recited it as silm (with kasrah, sukūn, and the nominative case). The author of Al-Bahr interprets this as meaning "We are, or you are, in a state of peace."

(A people unknown): He, peace be upon him, did not recognize them—either because the greeting they used was not the greeting of Islam, or because they were not among those he knew of people, or because their appearance and form differed from that of ordinary people.

(A people) is the predicate of an omitted subject. The majority hold that the intended meaning is "[You are] a people unknown," and that he, peace be upon him, said this to them in order to gain information, similar to when you say to someone you meet, "I do not know you," intending for them to introduce themselves and describe who they are.

Some researchers have gone to the view that what is apparent is that the intended meaning is "These are a people unknown," and that he, peace be upon him, said this to himself or to those who were with him from among his followers and servants, without making the guests aware of it. This is more appropriate for his state, peace be upon him, because addressing guests with such a statement would cause a level of alienation, and his purpose in saying it was for them to reveal their state, perhaps so that he might alleviate their [stranger] status. Furthermore, had his intent been to address them, they would have revealed their identities upon that statement, yet he did not [immediately] proceed to the preparations for hospitality [until they revealed themselves].