Should a Muslim who smiles during prayer complete it, or interrupt and repeat it?

A Muslim should have khushu' (devotion/humility) in their prayer, as it is the essence of prayer, and Allah has praised the believers for it. Smiling during prayer does not invalidate it according to the majority of scholars, such as Ibn al-Mundhir, Ibn Qudamah, Ibn Taymiyyah, Al-Nawawi, and Al-Buhuti, unlike loud laughter (qahqahah) which invalidates prayer by consensus. Therefore, the worshipper should complete their prayer and not cut it short, and they must avoid anything that diminishes khushu'.