Hadith 385
'Umar bin al-Khattab reported: The Messenger of Allah (ﷺ) said: When the Mu'adhdhin says: Allah is the Greatest, Allah is the Greatest, and one of you should make this response: Allah is the Greatest, Allah is the Greatest; (and when the Mu'adhdhin) says: I testify that there is no god but Allah, one should respond: I testify that there is no god but Allah, and when he says: I testify that Muhammad is the Messenger of Allah, one should make a response: I testify that Muhammad is Allah's Messenger. When he (the Mu'adhdhin) says: Come to prayer, one should make a response: There is no might and no power except with Allah. When he (the Mu'adhdhin) says: Come to salvation, one should respond: There is no might and no power except with Allah, and when he (the Mu'adhdhin) says: Allah is the Greatest, Allah is the Greatest, then make a response: Allah is the Greatest, Allah is the Greatest. When he (the Mu'adhdhin) says: There is no god but Allah, and he who makes a response from the heart: There is no god but Allah, he will enter Paradise.
Hadith 1100
'Umar (RA) reported Allah's Messenger (ﷺ) as saying: When the night approaches and the day retreates and the sun sinks down, then the observer of the fast should break it. Ibn Numair made no mention of the word "then".