Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says that I heard the Messenger of Allah (peace and blessings be upon him) say:“ «لَا إِلَـٰهَ إِلَّا اللَّـهُ» is the most virtuous remembrance, and «اَلْحَمْدُ لِلّٰهِ» is the best word of gratitude.”

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The most excellent word is that which I and the previous prophets have said on the evening of the Day of Arafah (and it is this): «لا إله إلا الله وحده لا شريك له، له الملك وله الحمد، وهو على كل شيء قدير» ... 'There is no deity worthy of worship except Allah, He is alone, He has no partner, to Him belongs the dominion, to Him belongs all praise, and He has power over all things.'"