Full Eph 6:18. The verse is grammatically a participial clause, not a list-item: "with all prayer and supplication praying at all seasons in the Spirit, and watching thereunto in all perseverance and supplication for all the saints" (ASV). Treating prayer as a discrete seventh armor-element flattens the Greek grammar and obscures its actual function: prayer is the continuous vigilance and disposition in which the other six pieces are worn.
Matthew Henry catches the same structural point from a different angle: "Prayer must buckle on all the other parts of our Christian armour... We must pray with all prayer and supplication, with all kinds of prayer: public, private, and secret, social and solitary, solemn and sudden; with all the parts of prayer: confession of sin, petition for mercy, and thanksgivings for favours received.", Matthew Henry, Commentary on the Whole Bible (1710), on Eph 6:17–18
This posture is where the armor passage meets the wider practice of spiritual warfare. Within the roster's spiritual-warfare-prayer stream, Dutch Sheets frames intercession as active co-laboring with God rather than passive request (Intercessory Prayer, 1996), while Chip Ingram works this exact passage into an accessible six-piece discipleship framework for ordinary believers (The Invisible War, 2006), the same posture, pitched at two different registers, strategic and pastoral.