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.
If a person experiences intrusive thoughts (whispers), he should not pay attention to them, as getting carried with them only strengthens their hold. There is no harm in consulting psychological specialists to treat them.
What one is required to believe in this regard is well-known and simple, and does not require overthinking or anxiety: it is the belief that Allah, the Exalted, is the First - there is nothing before Him - and that He is the Creator of all things. Allah says: {Say, 'Allah is the Creator of all things.'} [Quran 13: 16]
Allah, the Exalted, also says: {He is the First and the Last, the Most High and the Most Near, and He is, of all things, Knowing.} [Quran 56: 3]
In the Hadith reported in Sahih Muslim, the Prophet, salallaahu 'alayhi wa sallam, said: “You are the First, and there is nothing before You.”
Allah knows best.