Why do we bear witness, stating the Shahadah, when we do not see Allah or Muhammad with our own eyes?

Testimony is informing about what a person knows, and it is not exclusive to what one sees with their own eyes. The proof for this is the Almighty Allah's saying, on the tongue of Yusuf's brothers: ﴿And we do not testify except to what we know.﴾

There are three ways to acquire knowledge: the indication of reason, the indication of the senses, and the report of a truthful person. Any of these ways that provides a person with knowledge, their informing about it is called testimony.

The assumption that testimony is confined to eyewitness testimony is what causes the problem. However, testimony is broader than that; it is informing about what a person knows, whether they learned it through reason, through the senses, or through the report of a truthful person. Therefore, informing about the oneness of Allah and the prophethood of Muhammad, peace be upon him, which is based on rational and transmitted evidence, is called testimony without any problem.