What is the Holy Spirit mentioned in verse 87 of Surat Al-Baqarah: "And We did give unto Jesus, son of Mary, Clear Signs and did strengthen him with the Holy Spirit"?

The Holy Spirit is Gabriel, peace be upon him. This is supported by Quranic verses such as: "The Trustworthy Spirit has descended with it" (Quran 26:193) and "Then We sent to her Our Spirit" (Quran 19:17), and by noble prophetic traditions, such as the Prophet's supplication for Hassan ibn Thabit: "O Allah, support him with the Holy Spirit." Allah Almighty supported the prophets with the Holy Spirit, and scholars have mentioned that this is not exclusive to the Christ, peace be upon him.