The Prophet, sallallaahu ‘alayhi wa sallam, said, "'Laa Hawla wa laa Quwwata illaa Billaah Al-'Aliyy Al-'Atheem' is a door from one of the doors of Paradise.Whoever says 'Laa Hawla wa laa Quwwata illaa Billaah', an angel descends to give good health/brings a cure for that person." (Tirmidhi). Is this Saheeh (authentic)?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The first part of the hadeeth: "Laa Hawla wa laa Quwwata illaa Billah Al-'Aliyy Al-'Atheem (which means: There is no might and power but that of Allah, The Exalted, The Great)" was narrated by At-Tirmithi on the authority of Qays ibn Sa‘d ibn ‘Ubaadah . He narrated that his father offered him to the Prophet, sallallaahu ‘alayhi wa sallam, to serve him. He said, "The Prophet, sallallaahu ‘alayhi wa sallam, passed by me, and I had just performed the prayer; he, sallallaahu ‘alayhi wa sallam, poked me with his foot and said, 'Should I not direct you to a gate from the gates of Paradise?' I said, 'Yes.' He, sallallaahu ‘alayhi wa sallam, said, 'Laa Hawla wa laa Quwwata illaa Billah.'" [At-Tirmithi]

Shaykh Al-Albaani classified it as Saheeh (sound).

As for the part reading: "Whoever says, 'Laa Hawla wa laa Quwwata illaa Billah,' an angel descends to give good health (brings a cure for that person)," we could not find it in the Hadeeth collections of At-Tirmithi or other Hadeeth scholars. It seems that it has no basis in the Sunnah.

Allah knows best.