The best of supplications is the supplication on the day of AAarafah and the best which I and the Prophets before me have said (is):
Chapter
The Day of AAarafah
2 entries
لَا إِلَهَ إِلَّا اللهُ وَحْدَهُ لَا شَريكَ لَهُ، لَهُ المُلْكُ ولَهُ الحَمْدُ وهُوَ عَلَى كُلِّ شَيْءٍ قَديرٌ.
La ilaha illal-lahu wahdahu la shareeka lah, lahul-mulku walahul-hamd, wahuwa AAala kulli shayin qadeer.
Translation
None has the right to be worshipped except Allah, alone, without partner. To Him belongs all praise and sovereignty and He is over all things omnipotent.