What is Du'a Kumayl, and who is Kumayl? Is the supplication from Al-Khidr, and did Ali ibn Abi Talib teach it to Kumayl? Is there anything specific regarding its recitation?

This supplication attributed to Al-Khidr (peace be upon him) – "O He whom no hearing distracts from another hearing…" – was mentioned by Al-Ajlouni from Al-Khatib, and by Ibn Asakir from Ali ibn Abi Talib, who stated that Al-Khidr said it and promised forgiveness of sins for anyone who recites it after the prescribed prayer. However, Ibn Hajar ruled it to be weak.

It appears that the reported merits of this supplication are not authentic for several reasons: 1. Ibn Hajar ruled it to be weak. 2. Its absence from the well-known books of Sunnah, despite the great reward attributed to it. 3. Its inclusion of abundant reward for little effort, which is one of the signs of a fabricated hadith.

It is better for a Muslim to use the supplications authentically reported from the Prophet (peace be upon him) after the obligatory prayers, such as: 1. Saying "Astaghfirullah" (I seek forgiveness from Allah) three times, then "Allahumma Antas-Salam wa minkas-Salam, tabarakta Ya Dhal-Jalali wal-Ikram" (O Allah, You are Peace, and from You comes peace. Blessed are You, O Possessor of Majesty and Honor). 2. Glorifying Allah (Tasbih), praising Allah (Tahmid), and exalting Allah (Takbir) thirty-three times each, and then completing the hundred by saying, "La ilaha illallahu wahdahu la sharika lahu, lahul-mulku wa lahul-hamdu wa huwa ala kulli shayin qadir" (There is no god but Allah, alone, without partner. To Him belongs all sovereignty and praise, and He is over all things competent). Whoever says this, his sins will be forgiven, even if they are like the foam of the sea.