Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that one night the Messenger of Allah (peace and blessings be upon him) delayed the Isha prayer so long that the people fell asleep, then woke up, then fell asleep again, then woke up. Then Sayyiduna Umar (may Allah be pleased with him) came and said: O Messenger of Allah, the prayer! So they all prayed. The narrator did not mention that they performed a fresh ablution.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11297