Indeed, We sent it/him down during the Night of Decree.
The pronoun "it/him" in this Verse refers to the Qur'aan.
al-'aluusi has related that there is an Ijmaa on this.
And he said that there is a weak opinion that it refers to Jibriil but this opinion is not to be considered.
al-haawi fii tafsiir al-Qur'aan al-Kariim
Volume 16 Page 370