Surah 98. Al-Bayinah, Ayah 1

I.e., idol-worshippers or animists (in the anthropological sense of this word) who have never had any revealed scripture to fall back upon.

The Clear Evidence was the holy Prophet himself, his life, his personality, and his teaching.

The People of the Book immediately referred to are the Jews and the Christians, who had received scriptures in the same line of prophecy in which came our holy Prophet. Their scriptures should have prepared them for the advent of the greatest and last of the Prophets. For the Jewish scriptures promised to the Jews, cousins or brethren to the Arabs, a prophet like Moses: "The Lord thy God will raise up unto thee a Prophet from the midst of thee, of thy brethren, like unto me; unto him ye shall hearken" (Deut, xviii. 15). And Christ promised a Comforter (John. xiv. 16; xv. 26; and xvi. 7; see my n. 5438 to lxi. 6) almost by name. The People of the Book fell from the true, straight, and standard religion, into devious ways, and would not come to the true Path until (they said) they were convinced by the arrival of the promised Prophet. But when the promised Prophet came in the person of Muhammad, they rejected him, because they really did not seek for Truth but only followed their own fancies and desires.

The Polytheists, the Pagans, had not previously believed in any scriptures. But yet, when clear evidence came to them, they should have believed. Yet they rejected the holy Prophet because they were not really searching for Truth, but were only following their own fancies and desires.