Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
It is not correct to say “under the wings of His mercy” if “His mercy” is intended to mean the attribute of Allah, Exalted be He, because the matter of the divine attributes is based solely on revelation. No attribute may be affirmed for Allah except what is established in the Qur’an and Sunnah. However, if what is intended is a created mercy that is among the effects of His mercy, such as rain and the like, then there appears to be no objection to the expression. When there is ambiguity, it is preferable to avoid expressions that are open to multiple or unclear meanings.
Mercy is one of Allah’s attributes established by the Qur’an and Sunnah, just as Al-Rahman (the Most Merciful) and Al-Rahim (the Especially Merciful) are among His Most Beautiful Names.
Allah says:
“All praise is for Allah, Lord of all worlds, the Most Merciful, the Especially Merciful.”
[Al-Fatihah 1:1–2]
And He, Glorified be He, says:
“It is they who hope for Allah’s mercy, and Allah is All-Forgiving, Most Merciful.”
[Al-Baqarah 2:218]
In the two Sahih collections, Abu Hurayrah, may Allah be pleased with him, reported that the Prophet ﷺ said:
“When Allah created the creation, He wrote in a Book, which is with Him above the Throne: ‘Indeed, My mercy prevails over My wrath.’”
Narrated by al-Bukhari (3194) and Muslim (2751).
Mercy attributed to Allah, Exalted be He, may refer to Allah’s attribute, or it may refer to a created thing that is among the effects of His mercy.
An example of created mercy is found in the hadith in which Allah, Exalted be He, says to Paradise:
“You are only My mercy, through you I show mercy to whomever I will.”
Rain is another example, for Allah has called it mercy. He says:
“And He is the One who sends the winds as glad tidings before His mercy.”
[Al-A‘raf 7:57]
Ibn Taymiyyah, may Allah have mercy on him, explained that Allah is Al-Rahman and Al-Rahim by virtue of the mercy that is His attribute, while the mercy He creates is an effect of that mercy.
Thus, the word “mercy” may sometimes refer to the attribute itself and at other times to its created effect, depending on the context.
If a person who says “under the wings of His mercy” intends that the servant is under the divine attribute of mercy, then this expression should not be used. This is because affirming Allah’s attributes is based upon what has been revealed in the Qur’an and Sunnah, and it is not permissible to introduce new descriptions of Allah that have not been established in the revealed texts, even if the wording could linguistically bear such a meaning in Arabic.
The scholars have established that the matter of Allah’s attributes is based solely on revelation, so one must not go beyond what revelation has stated.
However, if what is meant by “mercy” is a created mercy, such as rain and the like, then there appears to be no objection in principle, because mercy here does not refer to Allah’s attribute that subsists in Him. Rather, it refers to one of His created things and an effect of His mercy.
Therefore, a distinction should be made between Allah’s mercy that is His attribute and a created mercy attributed to Allah as its Creator and Owner.
If an expression may carry both a correct and an incorrect meaning, or if the speaker’s intended meaning is unclear, then it is preferable to use clear expressions transmitted in the Qur’an and Sunnah.
Shaykh al-Islam Ibn Taymiyyah, may Allah have mercy on him, said:
“What is required is to use good expressions, namely the transmitted expressions that have come in the revealed texts, and to provide clarification regarding ambiguous and potentially confusing expressions.”
Accordingly, it is preferable to say, for example:
“We ask Allah to encompass us with His mercy,”
or:
“We ask Him to have mercy upon us through His mercy.”
These are expressions whose meanings are established and clear, rather than ambiguous expressions that have not been mentioned in the revealed texts.
The expression “under the wings of His mercy” should not be used if “His mercy” is intended to mean the attribute of Allah, Exalted be He, because Allah’s attributes are based solely on revelation, and none may be affirmed except what is established in the Qur’an and Sunnah. However, if “mercy” refers to a created thing that is among the effects of His mercy, such as rain, then there appears to be no objection. When the intended meaning is unclear, it is preferable to avoid the expression and use clear, transmitted wording instead.
And Allah knows best.