"quiet prayer" is a correct and usable phrase in written English.
You could use it when describing someone uttering or expressing a prayer in a quiet or subdued manner. For example, "She bowed her head in quiet prayer to thank God for her blessings."
On the other a group of pilgrims from Iran sits in quiet prayer.
And his head rolled, blood flowed from the saber, and the red grass whispered a quiet prayer in its wake".
The airport's chapel offers a setting for quiet prayer and a chance to speak with a priest, minister or rabbi.
Here they throw bougainvillea and jasmine petals at the revered saint before tying tangerine and tomato coloured strings to its outer gates in quiet prayer to their deity.
Inside, the family marveled at the soaring apse and stained glass, snapped photos, and spent a moment in a pew in quiet prayer.
But almost nothing felt entirely familiar across the New York region as cheering crowds and quiet prayer commemorated the first Memorial Day after the Sept. 11 attacks.
Ministers held quiet prayers.
Around the house, demonstrators celebrated with geysers of Champagne and quiet prayers over clenched rosaries.
It shows in the deadly, churchlike silence that pervades Fenway at the slightest sign of trouble, and it shows in the quiet prayers in the stands.
There were tears, loud wails, and quiet prayers as old neighbors joined hands with people who had driven in from Chicago and other nearby towns to pay their respects.
But instead of quiet prayers and reflection, the 50 anti-gun demonstrators who arrived at the store on Route 58 yesterday afternoon were confronted by more than 200 noisy counterdemonstrators who drowned out the vigil with chants and taunts.
