Does the prayer of one from whom words considered among the nullifiers of Islam were uttered, without his knowledge thereof, become invalid? And is his marriage considered void in this case?

A Muslim is excused by reason of ignorance regarding what he does not know to be forbidden. However, learning Tawheed (monotheism) and its nullifiers is obligatory. Therefore, whoever falls into shirk (associating partners with Allah) out of ignorance does not deserve punishment until proof is established against him. Apostasy is judged to be Islam simply by the act of prayer.