Surah 16

Surah 16:102

"Say: ‘The holy spirit has brought it down from your Lord in truth, to make firm those who believe, and as a guidance and good news for those who submit.’"

16.102 – The holy spirit has brought it down from your Lord in truth
In response to the accusation of inventing in verse 101, the messenger is commanded to say that the “holy spirit” brought him the substituted verse. A second response comes in verse 105: the “disbelievers” are lying (using the same verb as v. 101).
This is the last of only four occurrences of the expression “holy spirit” ( rūḥ al-qudus , lit. “the spirit of the holy”) in the Quran (also 2.87; 2.253; 5.110). In the three other occurrences, “holy spirit” is used only in connection with ‘Īsā.
What does the Quran mean by this expression? Muslim commentators came to identify “holy spirit” in the Quran with Gabriel. In 2.97, Gabriel ( jibrīl ) “brought it down on your heart.” If readers understand 2.97 to be in parallel with 16.102, they would tend to identify the holy spirit with Gabriel.
One consequence of these few and confusing references to the holy spirit is that there is no development in the Quran of the presence of God’s own spirit with people to, for example, “guide you into all truth” (John 16:8). A biblical understanding of God’s Holy Spirit could also have prevented the needless controversy of 61.6. When Jesus described to his disciples the “Counselor” who was to come after him, he clearly indicated that the Counselor was the Holy Spirit (John 14:26), not a human leader. See the comment at 61.6 on the “Holy Spirit” described by Jesus in the Gospel.

- from The Quran with Christian Commentary: A Guide to Understanding the Scripture of Islam