The disciples received the Father's words through Jesus and believed the Father sent him.

John 17:6–8

⁶I have manifested thy name unto the men which thou gavest me out of the world: thine they were, and thou gavest them me; and they have kept thy word.

⁷Now they have known that all things whatsoever thou hast given me are of thee.

⁸For I have given unto them the words which thou gavest me; and they have received them, and have known surely that I came out from thee, and they have believed that thou didst send me.