Narrated 'Abdullah bin Malik bin Buhaina: Whenever the Prophet ﷺ used to offer prayer he used to keep arms away (from the body) so that the whiteness of his armpits was visible.
The Prophet ﷺ also taught us about proper posture during prayer which includes keeping our backs straight and not slouching or leaning too much on one side or another. This helps us maintain focus on what we are saying in our prayers and keeps us mindful of Allah's presence throughout the entire prayer session. It also helps ensure that all parts of our body are properly aligned with each other which is important for proper worship according to Islamic teachings.
Finally, it is important for Muslims to remember that humility and modesty should be at the forefront when they are engaging in any form of worship including prayer as these qualities will help them stay focused on their relationship with Allah instead of getting distracted by worldly matters or physical appearances.