وَأَصْحَابِهِ
And upon his Companions.
The word ṣāḥib basically denotes one who accompanies another; its plural is aṣḥāb. In the familiar technical definition, a Companion is one who met the Prophet ﷺ as a believer and died upon Islam. Living in the same period or merely hearing about the Prophet does not establish this status.
Both the meeting and faith conditions matter. Meeting does not necessarily require years of companionship, although more restricted uses of ṣuḥbah are found in other scholarly discussions.
Praying for the Companions acknowledges their religious association, support for the Prophet's mission, and role in transmitting guidance to the community.