Surah 55. Ar-Rahman, Ayah 4

The term al-bayan - denoting "the means whereby a thing is [intellectually] circumscribed and made clear" (Raghib) - applies to both thought and speech inasmuch as it comprises the faculty of making a thing or an idea apparent to the mind and conceptually distinct from other things or ideas, as well as the power to express this cognition clearly in spoken or written language (Taj al-'Arus): hence, in the above context, "articulate thought and speech", recalling the "knowledge of all the names" (i.e., the faculty of conceptual thinking) with which man is endowed (see 2:31 and the corresponding note [23]).

Bayan: intelligent speech: power of expression: capacity to understand clearly the relations of things and to explain them. Allah has given this to man, and besides this revelation in man's own heart, has aided him with revelation in nature and revelation through prophets and messengers.