I hear there is an inyan not to pray in clothes that one slept in. I also heard the qualification that this is only for clothes meant for sleeping. (I don't have sources)
Would something like boxers and undershirt count under this rule?
For example, you are away for shabbat, but only have one undershirt. You sleep in it, but can't change it the next day. Is is better not to wear it to tefillah?