Although it is not mentioned in scripture, the Assumption of Mary has been a solidly held belief of our faith since apostolic times. It has been celebrated liturgically since the 6th century AD.
The Assumption of Mary was declared a dogma (a divinely revealed truth) of the Catholic Church by Pope Pius XII in 1950 when he proclaimed, in a document entitled Munificentissimus Deus, “The Immaculate Mother of God, the ever-virgin Mary, having completed the course of her earthly life, was assumed body and soul into heaven.”
Catholics worldwide meditate on the Assumption of Mary when praying the glorious mysteries of the Rosary, and on its feast day, August 15th. This prayer below can help put you in a fitting frame of mind when reflecting on this wondrous event:
Almighty and eternal God, who hast taken up into the glory of Heaven, with body and soul, the immaculate Virgin Mary, Mother of thy son: grant us, we pray, that we may always strive after heavenly things and thus merit to share in her glory. Amen.
Read more from the source: https://www.ourcatholicprayers.com/assumption-of-Mary.html