The Qur'an is full of references topromises of heaven for those who obey God, and hell for those who disobey. Although interpretations may differ, perhaps it could be taken as a sign that self-interest is ok: if God didn't expect you to act in your own self-interest, it seems he would not offer punishment/reward as your motivation. That is not to say that punishment/reward would be your only motivation; presumably love for God is a big factor. But punishment/reward is by far the most abundantly mentioned motivation, at least in the Qur'an.