قَالَ النَّبِيُّ صلى الله عليه وسلم: ((خَيْرُ الدُّعَاءِ دُعَاءُ يَوْمِ عَرَفَةَ، وَخَيْرُ مَا قُلْتُ أَنَا وَالنَّبيُّونَ مِنْ قَبْلِي: لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ)).
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): (La ilaha illal-lahu wahdahu la shareeka lah, lahul-mulku walahul-hamd, wahuwa AAala kulli shayin qadeer.)
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): (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.)
Source and references
Source edition: Fortress of the Muslim. Open source ↗