Sayyiduna Fadalah bin Ubayd al-Ansari (may Allah be pleased with him) narrates: I heard the Messenger of Allah (peace and blessings be upon him) say: "Islam is three houses: a lower one, an upper one, and an upper chamber. As for the lower house, it is Islam, which the generality of Muslims have entered; whichever of them is asked will say: 'I am a Muslim.' As for the upper house, it is the superiority of their deeds, some Muslims being better than others. And as for the upper chamber, it is jihad in the path of Allah; none attains it except the best of them."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15913