Is it permissible for the Sunni community in Germany to pray in a mosque affiliated with the Ahmadiyya Lahori group, especially given that the Imam is one of them, and considering that the Ahmadiyya Imam denies the belief in Ghulam Ahmed's prophethood and considers him merely a reformer?

The Qadianis, after the death of their founder Mirza Ghulam Ahmad, split into two factions: the "Ahmadiyya Qadiani" which believes that Ghulam Ahmad was a prophet, and the "Ahmadiyya Lahore" which claims he was a renewer (mujaddid). However, research has proven that their founder, Muhammad Ali, believed in his prophethood but showed otherwise to deceive Muslims. Therefore, it is not enough for the Imam to deny Ghulam Ahmad's prophethood and consider him a renewer to prove his innocence from this deviant sect. Rather, he must disavow all their beliefs that contradict Islam, such as attributing human qualities to God, denying the finality of prophethood with our Master Muhammad (peace be upon him), preferring Qadian over Mecca, and permitting forbidden things. If the Imam truly disavows all of that, then he is not a Qadiani. It is not permissible to pray behind an Imam who belongs to this sect; instead, one must search for another mosque, because his prayer is invalid and is likely to mislead people.