This excerpt is taken from Sheikh al-Islam Imam Ibn Taymiyyah's book Al-Jawab al-Bahir fi Zuwar al-Maqabir, translated by Sheikh Ataullah Saqib.
Salawat (Blessings) on Common Muslims
There is no disagreement that the Noble Prophet Muhammad ﷺ himself used to pray for mercy for others. Allah Almighty says:
وَصَلِّ عَلَيْهِمْ ۖ
"Invoke mercy upon them."
Reference: (9-At-Tawbah:103)
In Sahihayn, it is narrated that the Noble Prophet ﷺ prayed:
اللهم صل على آل أبى أوفى
"O Allah! Send mercy upon the family of Abi Awfa."
Reference: (Sahih Bukhari, Book of Zakat: Chapter on the Imam's Prayer and His Supplication for the One Giving Charity, Hadith: 1497; Sahih Muslim, Book of Zakat: Chapter on Supplication for the One Who Brings Charity, Hadith: 1078)
Once a woman came and said, "O Messenger of Allah! Pray for me and my husband." So he prayed:
صلى الله عليك وعلى زوجك
"May Allah send mercy upon you and your husband."
Reference: (Musnad Ahmad 3/398; Sunan Abi Dawood, Book of Witr: Chapter on Praying for One Other Than the Prophet, Hadith: 1533)
Salawat (Blessings) on the Family of the Noble Prophet ﷺ
There is no disagreement that the Prophet Muhammad ﷺ used to supplicate for mercy for his family in the same way he taught the Ummah. His teaching words are:
اللَّهُمَّ صَلِّ عَلَىٰ مُحَمَّدٍ وَعَلَىٰ آلِ مُحَمَّدٍ كَمَا صَلَّيْتَ عَلَىٰ إِبْرَاهِيمَ وَعَلَىٰ آلِ إِبْرَاهِيمَ إِنَّكَ حَمِيدٌ مَجِيدٌ اللَّهُمَّ بَارِكْ عَلَىٰ مُحَمَّدٍ وَعَلَىٰ آلِ مُحَمَّدٍ كَمَا بَارَكْتَ عَلَىٰ إِبْرَاهِيمَ وَعَلَىٰ آلِ إِبْرَاهِيمَ إِنَّكَ حَمِيدٌ مَجِيدٌ
"O Allah! Send mercy upon Muhammad and his family as You sent mercy upon Ibrahim and his family. Indeed, You are Praiseworthy and Glorious. And send blessings upon Muhammad and his family as You sent blessings upon Ibrahim and his family. Indeed, You are Praiseworthy and Glorious."
Reference: (Sahih Bukhari, Book of Prophetic Narrations: Chapter 10, Hadith: 3370; Sahih Muslim, Book of Prayer: Chapter on praying upon the Prophet after Tashahhud, Hadith: 408)
If a person individually says Salat (prayer) upon someone, such as "Sallallahu alayhi Abi Bakr," "Sallallahu alayhi Umar," "Sallallahu alayhi Uthman," or "Sallallahu alayhi Ali," there are two cases:
➊ The first is that it is permissible because Imam Ahmad used the statement of Sayyidina Ali (may Allah be pleased with him) as evidence, in which he said to Sayyidina Umar (may Allah be pleased with him), "Sallallahu alayka." Imam Ahmad's majority companions, such as Qadi Abu Ya'la, Ibn Aqil, and Sheikh Abdul Qadir, also prefer this view. They did not mention any disagreement in this matter.
➋ The second case is prohibition. A group among the followers of Imam Malik and Imam Shafi'i have written that it is prohibited. Our ancestor Abu al-Barakat also said the same in his book Kabir. Their evidence is the statement of Sayyidina Ibn Abbas (may Allah be pleased with both of them), in which he said:
لا أعلم الصلوة تنبغي من أحد على أحد إلا على رسول الله
"I do not consider anyone other than the Noble Messenger deserving of Salat upon them."
Reference: Nafdh al-Salat 'ala al-Nabi ﷺ by Qadi Ismail
They also say that those who prohibit sending Salat upon anyone other than the Messenger of Allah, their viewpoint is that if Salat is sent upon anyone other than the Messenger of Allah, the one truly deserving of it is the Messenger of Allah himself. However, by extension, it can be applied to others because something that is not permissible primarily can be permissible by extension.
Sending blessings upon the Messenger of Allah is obligatory, and for common Muslims it is recommended
Those who have deemed it permissible say that there is no negation of it in the Book and Sunnah. They argue from the statements of Sayyiduna Umar (may Allah be pleased with him) and Sayyiduna Ali (may Allah be pleased with him) and also say that it is not obligatory for anyone except the Messenger of Allah. The obligation for him is specific due to the command, not due to permissibility or recommendation.
They also give a proof that angels pray for the believers, as narrated in Sahihain, the Noble Prophet (peace be upon him) said:
أن الملائكة تصلى على أحدكم ما دام فى مصلاه
"Indeed, the angels continue to pray for mercy for any person among you as long as he remains sitting in his place of prayer."
Reference: (Sahih Bukhari, Book of Adhan: Chapter on the Virtue of Congregational Prayer, Hadith: 247; Sahih Muslim, Book of Mosques: Chapter on the Virtue of the Prescribed Prayer in Congregation, Hadith: 272/649)
Therefore, when angels pray for mercy for a believer and Allah Almighty sends down His mercy, how can it be impermissible for a believer not to pray for mercy for his believing brother?
Reformation of the Innovators
As for the statement of Ibn Abbas, may Allah be pleased with them both: This is for those innovators who, leaving the general believers aside, only advocate sending blessings upon Sayyiduna Ali, may Allah be pleased with him, which is unanimously considered an innovation. These innovators do not supplicate mercy for all members of Bani Hashim, nor for Hasan, Ali, Husayn, and all their wives. Whereas these words are explicitly present in Sahihayn:
اللهم صل على محمد وعلى أزواجه وذريته
"O Allah! Send mercy upon Muhammad and Your purified wives and Your offspring."
Reference: (Sahih Bukhari, Book of Prophetic Traditions: Chapter 10, Hadith: 326; Sahih Muslim, Book of Prayer: Chapter on Sending Blessings upon the Prophet after Tashahhud, Hadith: 407)
After this narration, no one has any justification to supplicate for some members of the Ahl al-Bayt while excluding others, or to restrict supplication only to certain believers.
