[al-Mā’idah: 41],
“O Messenger, convey what has been revealed to you from your Lord.” [al-Mā’idah: 67]
“O you wrapped in garments!” [al-Muzzammil: 1]
“O you covered in a cloak!” [al-Muddaththir: 1]
We have even greater reason, then, to observe proper etiquette when calling upon him and addressing him.
When speaking about him, however, we say: “I bear witness that there is no god but Allah, and I bear witness that Muhammad is the Messenger of Allah.” We also say: “Muhammad is the Messenger of Allah and the Seal of the Prophets.” Thus, we speak about him using his name, just as Allah, glorified be He, did when speaking about him, peace and blessings be upon him:
“Muhammad is not the father of any of your men, but he is the Messenger of Allah and the Seal of the Prophets.” [al-Ahzāb: 40]
He also said:
“Muhammad is the Messenger of Allah, and those with him are firm against the disbelievers and merciful among themselves. You see them bowing and prostrating.” [al-Fath: 29]
And He said:
“Muhammad is no more than a messenger; messengers have passed away before him.” [Āl ‘Imrān: 144]
And He said:
“And those who believe, do righteous deeds, and believe in what has been sent down to Muhammad.” [Muhammad: 2]
The distinction between directly addressing someone and speaking about him is established by both revelation and reason. This clarifies the distinction between the Most Beautiful Names by which Allah is invoked and the expressions used to speak about Him, exalted be He, that convey established truths: affirming the attributes of perfection that befit Him, glorified be He, and denying the flaws and imperfections from which He, mighty and majestic, is free. For He is the Sovereign, the Most Holy, the Source of Peace. Glory be to Him, and exalted is He far above what the wrongdoers say.
Allah Most High said:
“To Allah belong the Most Beautiful Names, so call upon Him by them, and leave those who deviate concerning His names.” [al-A‘rāf: 180]
Yet He also said:
“Say, ‘What thing is greatest in testimony?’ Say, ‘Allah is a witness between me and you.’” [al-An‘ām: 19]
But one does not say in supplication: “O Thing!”