Assalamu Alaikum Wa Rahmatullahi wa barakatuhu.Is it Haram to enter a Ahmadi masjid without any necessity but just to know what they believe in.Alhamdulilah and In'sha'Allah I'm a firm believer in Islam and don't think and Insha'Allah it won't effect my Imaan if I went in the Masjid of the Ahmadi JazzakAllah Khair

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

We have talked in previous fatwas about the Qadianis sect that is called the Ahmadiyya in Fatwa 88413. Refer to it to benefit. As for entering their mosques, it is permissible in terms of the basic principle, especially if the entry did not result in participating in their sin, nor seeing it and witnessing it without denial. As for your saying that they will not affect your faith, we advise you as indicated by the purified Sunnah of the desirability of fleeing from the places of temptation, even if the Muslim thinks that he will not be affected by it. In an authentic hadeeth, the Prophet said: “Let him who hears of the Dajjal (Antichrist) go far from him for I swear by Allah that a man will come to him thinking he is a believer and follow him because of confused ideas roused in him by him.” [Abu Dawood in his Sunan].

Ibn Battah al-Akbari said in al-Ibanah al-Kubra, following this hadeeth: “What I have is that whoever sits with him and talks to him is afraid of harm in religion or in the world, and an increase in enmity and hatred, so abandoning him and being far from him is better than being close to him. Because he preserves your slips, and he commands you in your right mind, and you do not deliver from the bad consequence of his mixture.” [End Of Quote].

Allah knows best.