How authentic is the Hadith attributed to the Prophet, may Allah’s prayers and peace be upon him, which states that Allah Almighty will say to him on the Day of Resurrection: "Admit whomever you wish to Paradise and whomever you wish to Hellfire," and he will reply: "O Lord, You are more merciful to them than I am"?

The aforementioned hadith (definition) has not been found. However, it is mentioned in some narrations of the hadith of intercession that the Prophet (peace and blessings be upon him) said: "I kept returning to my Lord, the Almighty and Exalted, and I did not stand in any position except that I interceded, until Allah, the Almighty and Exalted, granted me that He said: 'O Muhammad, admit into your Ummah, from Allah’s creation, whoever testified that there is no god but Allah for a single day, sincerely, and died upon that.'" (Narrated by Ahmad). And Allah, the Most Glorified and Exalted, is merciful to His servants; He is more merciful to them than a mother is to her child, as stated in the hadith: "Allah is more merciful to His servants than this one (a mother) is to her child."