Ever Wonder What Early Muslims Knew About Imam Mahdi?

As-salamu alaykum, I've got a sincere question here that's been on my mind. It's pretty well-known that our beliefs about Imam Mahdi and Masih ad-Dajjal mostly come from hadith, since they aren't directly named in the Qur'an. But here's the thing: the first major, organized hadith collection, like Al-Muwatta, wasn't put together until about 120-130 years after the Prophet Muhammad (peace be upon him) passed away. So that got me thinking-what did Muslims in those very first generations after the Prophet actually believe about Imam Mahdi and the Dajjal? Like, if you were living in the first 100 years after the Prophet's time, what would you have understood or been taught about these figures? Just to be clear, I'm asking from a Sunni perspective that accepts the hadith tradition, not a Qur'an-only viewpoint. JazakAllah khair for any insights!