Q 8: How many are the conditions of worship?
A ---They are three.
First: Sincere determination which is a condition that goes with the act of worship itself.
Second: Sincerity of intention.
Third: Compatibility with Islamic Law (Shari 'ah) ordained by Allah.
The later two represent conditions for accepting an act of worship.
Reference: 200 FAQ On Muslims Belief - Shiekh Hafiz Ibn Ahmed Al Hakami