What is the ruling on breathing heavily while smiling during prayer?

Humility (khushu') is the spirit and essence of prayer. A smile does not invalidate it according to the majority of scholars, in contrast to laughter, which nullifies it by consensus. Nevertheless, it is preferable to suppress it, in pursuit of complete humility and to avoid reaching the point of laughter that invalidates the prayer. Smiling does not invalidate the prayer unless it reaches the level of cackling (qahqahah) with the emission of two letters, whether accompanied by breathing or not.