Well first of all I must say that, it would be stupid to pray to statue of Buddha, because Buddha was a simple man who just got enlightened. And Buddha means Enlightened one, so after we understood that Buddha was not a god and that Buddhism is not a religion but a teaching, we can understand why i said it would be stupid to prey to Buddha statue. If you ask me i think its not sin, unless you commit sin by hurting some other human with what you do. But some people would disagree i think.