by entailment, whereas it is always better for a term to point to its meaning explicitly than for it to do so only implicitly. This is made clear in the report of al-Barāʾ ibn ʿĀzib ⦗Allah be pleased with him⦘ when the Prophet ﷺ taught him the bedtime supplication. After al-Barāʾ repeated it he said, “…and in Your Messenger whom You have sent.” The Prophet ﷺ corrected him: “No; say, ‘…and in Your Prophet whom You have sent.’”⦗1⦘ The purpose was to make the reference to prophethood an explicit, textual indication.

There is a second reason: were one to say “the best Messenger,” the word messenger (rasūl) could apply both to the angelic messenger, Gabriel ⦗peace be upon him⦘, and to the human messenger, Muhammad ﷺ. Yet once the author explicitly names Muhammad, Gabriel is automatically ruled out.

The final alif in the verb ursilā (“was sent”) is what scholars of prosody call the “alif of unrestricted rhyme,” meaning the vowel that releases the rhyme.