Encomium on the Dormition of Mary, 4 — as quoted by Pitre (p 63); translation: Brian E. Daley, On the Dormition of Mary: Early Patristic Homilies (St Vladimir's Seminary Press, 1998)
When she [Mary] had completed her life's voyage happily…the one who gave the Law on Sinai, and who administered it from Sion, our God, summoned his ark of sanctification to be brought home from Zion to himself, just as David, her ancestor, had said of her in a psalm, 'Go up, O Lord, to the place of your rest, you and your ark of sanctification' (Ps 132:8). She is not carried like Moses' ark of old, drawn by oxen, but she is escorted and surrounded by an army, heaven's holy angels.
No freely usable English translation of this passage is online, so the note keeps Pitre's quotation and links to the full text. Translation: Brian E. Daley, On the Dormition of Mary: Early Patristic Homilies (St Vladimir's Seminary Press, 1998), as quoted by Pitre.
Why Pitre cites it
God 'summoned his ark of sanctification to be brought home from Zion to himself… She is not carried like Moses' ark of old, drawn by oxen, but escorted by heaven's holy angels.' One of the two Fathers Pius XII cited for the Assumption.