Allah, exalted is He, also says in the Quran:

“When We replace one sign with another—and Allah knows best what He reveals—they say, ‘You are nothing but a fabricator.’ No indeed; most of them do not know.” (Q 16:101)
(101)

“Say: ‘The Holy Spirit has brought it down from your Lord in truth.’” (Q 16:102)

He, exalted is He, also says:

“The Trustworthy Spirit has brought it down” (Q 26:193)
(193)

“to your heart so that you may be one of the warners.” (Q 26:194)

And He, exalted is He, says:

“Say: ‘Whoever is an enemy to Gabriel—it is he who has brought it down upon your heart by Allah’s permission, confirming what came before.’” (Q 2:97)

Thus, the Rūḥ al-Qudus (the Holy Spirit) who brought down the Quran from Allah is the Rūḥ al-Amīn (the Trustworthy Spirit); he is Jibrīl (Gabriel).

It is firmly established in the Ṣaḥīḥ that Abū Hurayrah heard the Prophet—may Allah bless him and grant him peace—say to Ḥassān ibn Thābit: “Respond on my behalf. O Allah, support him with the Holy Spirit.”