It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Plant many trees (of good deeds) in Paradise, for its water is sweet and its soil is fragrant, so plant as many of its trees as you can - (and the tree of Paradise is this phrase:) La hawla wa la quwwata illa billah (There is no power and no strength except with Allah)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13297