Is the supplication of Imam Ahmad ibn Hanbal authentic: "My Master, Your forbearance has emboldened this transgressor until he persecutes Your saints with beating and killing. O Allah, if the Qur'an is Your uncreated speech, then spare us his evil"? And is it permissible to supplicate to Allah Almighty with "My Master"?

Firstly:

The hadith of Mutarrif indicates that "Al-Sayyid" (the Master) is one of Allah's Beautiful Names, and it is permissible to supplicate to Allah using it. Although some scholars, such as Imam Malik, have differed on this matter. The preferred and safer approach is to supplicate using the formulations found in the Quran and Sunnah, such as "Ya Rabb" (O Lord) and "Allahumma" (O Allah).

Secondly:

Imam Ahmad's supplication, "My Master, let Your forbearance delude this wicked person...", which is mentioned in "Hilyat al-Awliya'", has a weak chain of transmission and is not authentically established. It also contains the phrase "I was astonished by his young age," which is objectionable because Imam Ahmad was elderly at the time of the alleged story.