The Ruling on Covering the Face and Leaning in Prayer
Question:
Is it permissible to cover the face during prayer, and also, is it permissible to lean against a wall or a pillar or the like?
Answer:
It is hated to cover the face in prayer and likewise, except for one who has an excuse. And it is not permissible in prayer - the obligation prayer - to lean against a wall or a pillar, since it is an obligatory on whoever can do so, to stand up straight without leaning, As for the non-obligatory prayers, there is no sin in that, because it is permissible to perform it sitting, and standing while leaning is better than sitting.
Source:
Shaykh `Abdul-`Azeez Bin Baz
Fatawa Islamiyah Vol. 2 Page 173