It is narrated from Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Sometimes two men set out for the mosque, then one of them returns with his prayer being better than the other's, if he is the more understanding of the two, and the other returns with his prayer not weighing even as much as a speck."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3955