Do Shi'as believe that the words of the Imams can abrogate the Quran? In what circumstances can this happen? If infallible Muhammad can abrogate the Quran with his own words, as many Sunnis believe, than that implies that the Imams can do the same, as they are also infallible. How do Twelvers and Ismailis differ on this question?

Ismailis pray three times a day at fixed times based on the clock. During their prayers, they read, in congregation (or individually), some sort of book which they call a "du'a book." I don't know much about this book; it seems it has six chapters, the first being Surah Al-Fatiha from the Qur'an, and the last containing the names of all 40-50+ of their imams (ending with the living imam). How exactly was this book compiled, and does it change or remain unchanged throughout the ages?

In Sunni Islam, there's a concept of *zakah* -- 2.5% (1/40) of your savings saved for a year need to be given to the poor in eight groups, which are outlined in *ayah az-zakah* (The Ayah of Zakah). This is well understood. I know some people who are Ismailis. I have heard them talking about a similar concept, except that it is one eighth (12.5%), and apparently it also applies to cooked food and other things. My question is, **what is this called and what is the "fiqh" of it?**