نَزَلَ بِهِ الرُّوحُ الْأَمِينُ فَعَلَّمَهُ سَيِّدَ الْمُرْسَلِينَ مُحَمَّدًا صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ
The trustworthy Spirit brought this speech down and conveyed it to Muhammad ﷺ, the leader of the messengers.
Al-Ruh al-Amin is Gabriel. He transmitted Allah's revelation to the Messenger ﷺ as a trusted angel; he was neither its creator nor its independent author. The Messenger conveyed that revelation to humankind.