O Messenger of Allah, I could not offer the ‘Asr prayer till the sun had set. The Prophet (may Allah's peace and blessings be upon him) said: By Allah! I have not yet prayed it either. So we went to But-hān, and he performed ablution and so did we, and then he offered the ‘Asr prayer after the sun had set and then followed it with the Maghrib prayer

‘Umar ibn al-Khattāb (may Allah be pleased with him) came to the Prophet (may Allah's peace and blessings be upon him) on the Day of the battle of the Trench after the sun had set, and he was cursing the disbelievers of Quraysh, because they had distracted him from offering the ‘Asr prayer, and he could not pray it until after the sun had set. So the Prophet (may Allah's peace and blessings be upon him) swore by Allah, and he is the truthful, that he too had not yet prayed it, in order to calm ‘Umar (may Allah be pleased with him) because it was hard for him.
Then the Prophet (may Allah's peace and blessings be upon him) got up and performed ablution, and the Companions did so too, and then he offered the ‘Asr prayer after the sun had set, followed by the Maghrib prayer.