Sunan an-Nasa'i, Volume 1, Book 6, Hadith 582 (DarusSalam) ⓘ

'Imran bin Hudair said: "I asked Lahiq about the two Rak'ahs before sunset. He said: "Abdullah bin Az-Zubair used to pray them, and Mu'awiyah sent word to him asking: 'What are these two Rak'ahs at sunset?' He had to refer to Umm Salamah, and Umm Salamah said: 'The Messenger of Allah used to pray two Rak'ahs before 'Asr, then he was distracted and did not pray them, so he prayed them when the sun set, and I never saw him pray them before or after that.'"

أَخْبَرَنَا عُثْمَانُ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، قَالَ أَنْبَأَنَا أَبِي قَالَ، حَدَّثَنَا عِمْرَانُ بْنُ حُدَيْرٍ، قَالَ سَأَلْتُ لاَحِقًا عَنِ الرَّكْعَتَيْنِ، قَبْلَ غُرُوبِ الشَّمْسِ فَقَالَ كَانَ عَبْدُ اللَّهِ بْنُ الزُّبَيْرِ يُصَلِّيهِمَا فَأَرْسَلَ إِلَيْهِ مُعَاوِيَةُ مَا هَاتَانِ الرَّكْعَتَانِ عِنْدَ غُرُوبِ الشَّمْسِ فَاضْطَرَّ الْحَدِيثَ إِلَى أُمِّ سَلَمَةَ فَقَالَتْ أُمُّ سَلَمَةَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُصَلِّي رَكْعَتَيْنِ قَبْلَ الْعَصْرِ فَشُغِلَ عَنْهُمَا فَرَكَعَهُمَا حِينَ غَابَتِ الشَّمْسُ فَلَمْ أَرَهُ يُصَلِّيهِمَا قَبْلُ وَلاَ بَعْدُ ‏.‏