that the Messenger of Allah ﷺ said, "The best dua is dua on the day of Arafa, and the best thing that I or the Prophets before me have said is 'There is no god but Allah, alone, without any partner' (La ilaha illa'llah, wahdahu la sharika lah.)"
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ أَفْضَلُ الدُّعَاءِ دُعَاءُ يَوْمِ عَرَفَةَ وَأَفْضَلُ مَا قُلْتُ أَنَا وَالنَّبِيُّونَ مِنْ قَبْلِي لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ