Ja'far (may Allah have mercy on him) says that when the Messenger of Allah (peace and blessings be upon him) mentioned the Hour, his anger would intensify, his voice would rise and his cheeks would turn red, as though he (peace and blessings be upon him) were warning of an army about to attack in the morning or the evening.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5755