I want to know towards which ayatollah should i look for masala related to ehtiyate wajib from ayatollah sistani.

and what does exactly difference is between wajib and ehtiyate wajib ?

1. Wãjib: means obligatory, necessary, incumbent. An act which must be performed. One will be punished for neglecting a wajib act, e.g., the daily prayers.

Ihtiyãt wãjib: Sometimes you might see the term “ihtiyãt wãjib” in the decrees of the mujtahids. It means “precautionarily obligatory” and its significance is the same as that of the wâjib with one difference: wherever the mujtahid says that “it is precautionarily obligatory,” you have the option of leaving his opinion in that particular problem and following the opinion of the second best mujtahid provided the second mujtahid has a different opinion.