Tafsir of Al-Hijr 15:10

"And certainly We sent"—meaning messengers, as has been narrated from Ibn Abbas. The reason it is not explicitly mentioned is the obviousness of its indication.

"From before you"—[this phrase] is connected to "sent" or to an omitted term that functions as an adjective for the omitted object; that is, "messengers existing from before you."

"Among the factions of the former peoples"—meaning their groups, as stated by al-Hasan and al-Kalbi; al-Zajjaj held the same view. Shiya' (factions), like ashya', is the plural of shi'ah, which refers to a group or community united upon a path and a school of thought. It is derived from sha'a (transitive), meaning "to follow," because some members of the group support and follow others. Shi'ah is also applied to helpers and partisans. The origin of this, according to what has been said, is from al-shiya' (with a kasrah or fathah on the shin), which refers to small firewood used to kindle larger pieces. The relevance of this [etymology] is evident regarding the second usage, and regarding the first, it is because a follower, by virtue of being a follower, is attached to the one he follows. Its genitive construction with "the former" is, according to al-Farra', an addition of the qualified to its quality, and according to the Basrans, it is a case of the omitted qualified; that is, "factions of the former nations." The prepositional phrase is connected to "We sent."

The meaning of sending messengers "in" the factions is the appointment of each of them as a messenger among a group of those factions so that they might follow him in all that he commands and prohibits regarding the affairs of religion. It is as if, had "to" been used instead of "in," this intended meaning would not have been apparent. It has been said that the reason for turning away from "to" toward "in" is to indicate a greater degree of establishment and authority. Some have claimed that the prepositional phrase is connected to an omitted term which is an adjective for the implied object, or is a state (hal), but its remoteness is not hidden.