The belief in the corporeal assumption of Mary is founded on the apocryphal treatise De Obitu S. Dominae, bearing the name of St. John, which belongs however to the fourth or fifth century. It is also found in the book De Transitu Virginis, falsely ascribed to St. Melito of Sardis, and in a spurious letter attributed to St. Denis the Areopagite. If we consult genuine writings in the East, it is mentioned in the sermons of St. Andrew of Crete, St. John Damascene, St. Modestus of Jerusalem and others. In the West, St. Gregory of Tours (De gloria mart., I, iv) mentions it first. The sermons of St. Jerome and St. Augustine for this feast, however, are spurious. St. John of Damascus (P. G., I, 96) thus formulates the tradition of the Church of Jerusalem:

St. Juvenal, Bishop of Jerusalem, at the Council of Chalcedon (451), made known to the Emperor Marcian and Pulcheria, who wished to possess the body of the Mother of God, that Mary died in the presence of all the Apostles, but that her tomb, when opened, upon the request of St. Thomas, was found empty; wherefrom the Apostles concluded that the body was taken up to heaven.

Today, the belief in the corporeal assumption of Mary is universal in the East and in the West; according to Benedict XIV (De Festis B.V.M., I, viii, 18) it is a probable opinion, which to deny were impious and blasphemous.

...Catholic Encyclopedia