The best supplication offered on the Day of ‘arafaat is that of the Prophet Muhammad (peace be upon him)
Laa ilaaha illallaahu wahdahu laa shareeka lah, lahul-mulku walahul-hamdu wahuwa ‘ala kulli shay-in qadeer
(There is no true God worthy of being worshipped except Allaah, alone, without any partners, to Him belongs the Kingdom, and all-praise is due to Him, and He is able to do all things).
Source : Hajj and Tawheed by Dr. Saleh as-Saleh ( Pg 25)
