A litter fixed on an animal follows the rules of prayer on the animal whether the animal is moving or standing.
But if the litter or platform is supported down to stable ground so that its base becomes effectively connected to the earth, it takes the ruling of the ground. In that case a Fard prayer can be performed there standing.
The legal issue is therefore not simply 'vehicle versus no vehicle'; stability and connection to the ground matter.
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Voluntary Prayer Sitting or Riding — and Prayer on a Mount
A litter fixed on an animal follows the rules of prayer on the animal whether the animal is moving or standing.
But if the litter or platform is supported down to stable ground so that its base becomes effectively connected to the earth, it takes the ruling of the ground. In that case a Fard prayer can be performed there standing.
The legal issue is therefore not simply 'vehicle versus no vehicle'; stability and connection to the ground matter.