Jabir (May Allah be pleased with him) reported:
I heard the Messenger of Allah (ﷺ) saying, "The best way to celebrate the remembrance of Allah is to say: La ilaha illallah (there is no true god except Allah)."[At-Tirmidhi].
App reference: Book 16, Hadith 30
Arabic/English book reference: Book 16, Hadith 1437