Musannaf Ibn Abi Shayba 13:2646

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Jabir, from ‘Amir, regarding a man who says to a man, "Do you have testimony?" and he says, "No," then he comes and testifies. He said: It is permissible.