Umayyad Caliphate:

According to tradition, the Umayyad family (also known as the Banu Abd-Shams) and Muhammad both descended from a common ancestor, Abd Manaf ibn Qusai, and they originally came from the city of Mecca. Muhammad descended from Abd Manāf via his son Hashim, while the Umayyads descended from Abd Manaf via a different son, Abd-Shams, whose son was Umayya. The two families are therefore considered to be different clans (those of Hashim and of Umayya, respectively) of the same tribe (that of the Quraish). However Muslim Shia historians suspect that Umayya was an adopted son of Abd Shams so he was not a blood relative of Abd Manaf ibn Qusai. Umayya was later discarded from the noble family. Sunni historians disagree with this and view Shia claims as nothing more than outright polemics due to their hostility to the Umayyad family in general. They point to the fact that the grand sons of Uthman, Zaid bin amr bin uthman bin affan and Abdullah bin Amr bin Uthman got married to the Sukaina and Fatima the daughters of Hussein son of Ali to show closeness of Banu hashem and Bani Ummayah.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who suspects that Muhammad was an adopted son?
unanswerable