It is narrated from Sayyiduna Mu'adh bin Anas al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The one who looks around in prayer, the one who laughs, and the one who cracks his fingers - they are all of one rank."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17555