It is narrated from Sayyiduna Fadalah bin Ubayd (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever wants the treasure of speech, let him hold fast to 'La hawla wa la quwwata illa billah' (There is no might and no power except with Allah)."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15864