as a muslim the answer is The Five Pillars, They are shahada (the belief in Islam), salat (the five daily prayers), zakat (giving to charity), sawm (fasting), and hajj (pilgrimage to Mecca at least once in a lifetime).
The legacy of Islam that I think is the most important is medicine. I say this because it is important to have medicine when you are sick or hurt. Also, it is important because some of the medicine they created back then we still use now.
