Assalaamu Alaikum

I'm so scared ams i need help In Shaa Allah.  For a long time now,  i have been suffering from huge waswas. It got really bad when i started feeling like i was saying things when i really wasn't. Or at other times,  i would feel get waswas and accidentally say something without intending to.

But two days ago something happened. I went to sleep and just as i was dropping off i suddenly recslled an awful waswas about Prophet Muhammad ( pbuh ).  I got very worried about this even as i was falling asleep. I woke up about an hour later and started thinking of this again. And then i can't explain it but my heart seemed to really harden. I felt like 'ok i don't care whatever'. And there was this huge urge to say the words and Astagfirullah I went ahead and six it. I knew even as i started to say it that this was wrong and i was aware whilst Saint it as well. No one would have heard it as it was just said without making any noise but i felt my tongue move. The second I finished,  I was filled with so much regret and horror. I was still lying in bed at this time as it had been just as i had woken up and hadn't even gotten up yet.

I'm in constant fear that i have become murthadh and that my nikah is void. I have spoken to two sheikhs and an usthaaza all of whom said this was due to waswas and it doesn't make me kufr. But i feel like i can't say waswas as an excuse for everything. I know what i did and i honestly feel like i did it on purpose. I don't know why as i absolutely hate the thought of it even. One sheikh did some Ruqya too to see if it was a jinn thing but i don't know if anything really happened.

In Shaa Allah i hope you can help me.