Should
      he fulfil his promise to an idol-worshipper?
Question

                What is the ruling on
      fulfilling a promise made to a Hindu, if a promise is made that does not
      involve going against the laws of Allaah?
Praise be to Allah.It is obligatory to fulfil
      any promises that do not go against the laws of Allaah. Allaah says
      (interpretation of the meaning):
“And
      fulfil (every) covenant. Verily, the covenant will be questioned about”
      [al-Israa’ 17:34]
Whether a promise is made to a Hindu or to anybody
      else it should be upheld so long as they do not go against the terms
      (under which they agreed to live under Muslim rule) or do any harm to
      Islam.
And
      Allaah is the Source of strength. May Allaah bless our Prophet Muhammad
      and his family and companions, and grant them peace.