Re: ismaili/aga khani
Crap I'm sorry I was mistaken, ayatullah's are the hujjats. They are the hujjat because when Imam Mahdi went into Ghaybat ul Kubra, it's reported he said, "And as for the [new] events, then return to those who deal with our traditions, for they are my proof upon you, and I am the proof of Allah." Sorry again.
Ok, Trulyurs posted the ahadith that I was going to post lol. The main point is, 12. I don't see any Sunni Khalifa's ending at 12, and surely you don't have 12 Imams.