Musnad Ahmad 1017:0

Narrated Buraydah al-Aslami: The Messenger of Allah (ﷺ) said: "Between us and the hypocrites is the witnessing of the 'Isha and the Fajr prayers, for they are unable to attend them." He (the Prophet) also said: "Whoever abandons the 'Asr prayer, his deeds are rendered void." He (the Prophet) also said: "Whoever leaves the prayer intentionally has disbelieved."