What is the ruling on leaning against the back of a chair in supererogatory prayers, while being able to stand, and what is its ruling in obligatory prayers for one who is unable to stand but is able to stand without leaning?

The worshipper must perform the obligatory prayer standing without leaning. If he is unable, he prays standing while leaning. If he is unable to do that, he prays sitting without leaning. And whoever prays sitting on a chair due to inability to stand, he should not lean his back against the chair if he is able not to do so, otherwise his prayer is invalid. As for the supererogatory prayer, the worshipper is permitted to perform it sitting or leaning even if capable of not leaning, and his prayer is valid, but the reward for standing is greater.