Mu'adh bin Abdullah bin Rafi' (may Allah have mercy on him) said: I was in a gathering in which Abdur-Rahman bin Umar, Abdullah bin Ja'far and Abdur-Rahman bin Abi Amrah (may Allah be pleased with them) were present. Ibn Abi Amrah said: I heard Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) say: I heard the Messenger of Allah (peace and blessings be upon him) say: "There are two words: nothing below the Throne stops one of them, and the other fills what is between the heaven and the earth: 'La ilaha illallah' (there is no god but Allah) and 'Allahu akbar' (Allah is the Greatest)." Ibn Umar (may Allah be pleased with him) asked Ibn Abi Amrah: "Did you yourself hear him say that?" He said: "Yes." The narrator said: Then Abdullah bin Umar (may Allah be pleased with him) wept until his beard was soaked with his tears, and then he said: "They are two words that we hold close to our hearts and are familiar with."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17470