Jami` at-Tirmidhi 3575

Mu`adh bin `Abdullah bin Khubaib, narrated from his father, who said:“We went out on a rainy and extremely dark night, looking for the Messenger of Allah (ﷺ), so that he could lead us in Salat.” He said: “So I met him and he (ﷺ) said: ‘Speak’ but I did not say anything. Then he (ﷺ) said: ‘Speak.’ But I did not say anything. He (ﷺ) said: ‘Speak.’ So I said: ‘What should I say?’ He (ﷺ) said: ‘Say: “Say: He is Allah, the One” and Al-Mu`awwidhatain, when you reach evening, and when you reach morning, three times, they will suffice you against everything.’”