He—may Allah have mercy on him—was asked about a man who said:

“When a servant supplicates, he should not say, ‘O Allah, O Most Merciful.’”

He answered:

Praise be to Allah.

There is no disagreement among Muslims that when a servant supplicates to his Lord, he may say, “O Allah, O Most Merciful.” This is necessarily known to be part of the religion of Islam. As Allah Most High says:

“Say, ‘Call upon Allah or call upon the Most Merciful. Whichever you call upon, to Him belong the Most Beautiful Names.’”

The Prophet—may Allah bless him and grant him peace—used to say in his supplication:

“O Allah, O Most Merciful.”

The polytheists then said, “Muhammad forbids us to call upon two gods, yet he calls upon two gods!” So Allah Most High said:

“Say, ‘Call upon Allah or call upon the Most Merciful. Whichever you call upon, to Him belong the Most Beautiful Names.’”

That is, the One being called upon is one God, even though His names are many. As Allah Most High says:

“To Allah belong the Most Beautiful Names, so call upon Him by them, and leave those who deviate concerning His names.”

Whoever denies that one may say, “O Allah, O Most Merciful,” must be called upon to repent. If he repents, that suffices; otherwise, he is to be put to death. And Allah knows best.