Whether visiting Durgahs (Umrah) and faith on Auliyaas is a sin or allowed?
Before I answer your specific question, I would like to clarify that `umrah is a form of Islamic worship, prescribed by God, it should not be compared to visiting Durgahs [graves of saints].
Visiting Durgahs, if not done with any religious reverence or veneration, is not prohibited per se. However, in view of the extreme reverence that such places have acquired in the eyes of the common Muslim, I do not like to visit these places and, for the same reason, would not recommend doing so either.
As far as the second part of your question, regarding ‘faith in auliyaas‘ is concerned, you will have to clarify the phrase ‘faith in auliyaas‘ to enable me to answer this question. In any case, there is no such thing as ‘faith in auliyaas‘ recommended or even recognized by Islam. Moreover, the fact that a particular person can be labeled as a ‘wali‘ (singular of ‘auliyaa‘) is also something, which can only be decided by the All-knowing. We have neither the absolute knowledge (about the person concerned) nor any reason to label anyone a ‘wali‘ of God.
22nd January 2000