Amr Ibn Shuaib (RA) narrates from his grandfather through his father: the Prophet (ﷺ) said the best dua is on Arafa day. The best words I and prophets before me ever said are these -
لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ، لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ
Transliteration
Laa 'ilaaha 'illAllahu wahdahu laa shareeka lahu, lahul-mulku wa lahul-hamdu wa Huwa 'alaa kulli shay'in Qadeer
Translation
None has the right to be worshipped except Allah, alone, without any partener. To Him belong all sovereignty and praise and He is over all things omnipotent.
حَدَّثَنَا أَبُو عَمْرٍو، مُسْلِمُ بْنُ عَمْرٍو الْحَذَّاءُ الْمَدِينِيُّ حَدَّثَنِي عَبْدُ اللَّهِ بْنُ نَافِعٍ، عَنْ حَمَّادِ بْنِ أَبِي حُمَيْدٍ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " خَيْرُ الدُّعَاءِ دُعَاءُ يَوْمِ عَرَفَةَ وَخَيْرُ مَا قُلْتُ أَنَا وَالنَّبِيُّونَ مِنْ قَبْلِي لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ " . قَالَ هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ مِنْ هَذَا الْوَجْهِ . وَحَمَّادُ بْنُ أَبِي حُمَيْدٍ هُوَ مُحَمَّدُ بْنُ أَبِي حُمَيْدٍ وَهُوَ أَبُو إِبْرَاهِيمَ الأَنْصَارِيُّ الْمَدَنِيُّ وَلَيْسَ هُوَ بِالْقَوِيِّ عِنْدَ أَهْلِ الْحَدِيثِ . `
Translation
Amr bin Shu`aib narrated from his father, from his grandfather, that the Prophet (ﷺ) said: “The best of supplication is the supplication of the Day of `Arafah. And the best of what I and the Prophets before me have said is: None has the right to be worshipped but Allah, Alone, without partner, to Him belongs all that exists, and to Him belongs the Praise, and He is powerful over all things. (Lā ilāha illallāh, waḥdahu lā sharīka lahu, lahul-mulku wa lahul-ḥamdu, wa huwa `alā kulli shai’in qadīr).’” Jami` at-Tirmidhi 3585 [Hasan the hadith. Tirmizi, 3585]
This arafah dua on Arafah day brings muslims near Allah's power and mercy. Strong zikr fills hearts with hope for forgiveness and blessings.
Muslims say la ilaha illallahu wahdahu la sharika lahu, lahu al-mulku wa lahu al-hamdu wa huwa 'ala kulli shay'in qadeer many times on arafat day. Tahleel, takbeer, and tahmeed are also said often for blessings.
In his arafah dua, Imam Hussain said: You are not hurt by your servants' sins. You don't need their obedience. Forgive me. All praise is for you, my God and my Lord.
For arafah amal, the dua is: O Lord, by your throne's power, your great name, and answered prayers - by your face's light - send blessings on Muhammad and his family.
Yes. Allah accepts dua very fast on Arafah day. This time is special for answers. People doing arafah fasting or standing at arafat get their prayers heard.
On arafat day say: O Allah, give me strength to stay steady, guide me, make me thankful, help me worship well, make my heart pure, my words true, and forgive me.