Not Sent as a Sign
Even if We sent down angels, made the dead speak, and gathered all things before them, they would still not believe unless Allah willed. But most of them are ignorant.
6:111And though We should send down the angels unto them, and the dead should speak unto them, and We should gather against them all things in array, they would not believe unless Allah so willed. Howbeit, most of them are ignorant.