complex search in Greek

You need to do a morph search in a Greek New Testament. Different NTs have different morphologies, and therefore different syntaxes. This one will work for NA27:

(lemma:πίστις BEFORE 1 WORD @NG) OR  (lemma:πίστις BEFORE 1 WORD @R??G)

You don't need to remember that @R??G is a genitive pronoun. Just type the @ sign and click on the dropdown menu.

You can also perform a Bible search using the following criteria. It gives the same results, but it's harder to construct:
<lemma = lbs/el/πίστις> BEFORE 1 WORDS (<lbs-morph+el ~ NG???>, <lbs-morph+el ~ R??G???>)