The best dua ever is the arafa day dua, and the best dua and words to say in this day is : ( La ilaha illallahu wahdahu la sharika lahu, lahul-mulku wa lahul-hamdu wa Huwa ‘ala kulli shai’in Qadir ), There is none worthy of worshipped in truth except Allah, alone, without any partner. The Kingdom and praise belong to Him and He has power over everything