Imām Bukhārī narrates: Abū Nu'aim narrated to us, he said: 'Abdul-Wāhid ibn Aiman narrated to us, he said: My father narrated to me, he heard from 'Ā'ishah, may Allāh be pleased with her, she said:
By the One who took the Messenger of Allāh ﷺ! He never at all abandoned the two rak'ahs after 'Asr, until he met Allāh, and he met Allāh the Exalted at the time when his body had become heavy from praying, and he used to pray most of his prayers sitting. 'Ā'ishah meant the two rak'ahs after the 'Asr prayer, and the Prophet ﷺ used to pray them, and he did not pray them in the mosque, out of fear that this would become difficult for his ummah, and he liked to make things easy for the ummah.
حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا عَبْدُ الْوَاحِدِ بْنُ أَيْمَنَ، قَالَ حَدَّثَنِي أَبِي أَنَّهُ، سَمِعَ عَائِشَةَ، قَالَتْ وَالَّذِي ذَهَبَ بِهِ مَا تَرَكَهُمَا حَتَّى لَقِيَ اللَّهَ، وَمَا لَقِيَ اللَّهَ تَعَالَى حَتَّى ثَقُلَ عَنِ الصَّلاَةِ، وَكَانَ يُصَلِّي كَثِيرًا مِنْ صَلاَتِهِ قَاعِدًا ـ تَعْنِي الرَّكْعَتَيْنِ بَعْدَ الْعَصْرِ ـ وَكَانَ النَّبِيُّ صلى الله عليه وسلم يُصَلِّيهِمَا، وَلاَ يُصَلِّيهِمَا فِي الْمَسْجِدِ مَخَافَةَ أَنْ يُثَقِّلَ عَلَى أُمَّتِهِ، وَكَانَ يُحِبُّ مَا يُخَفَّفُ عَنْهُمْ.
Reference: Sahih Al Bukhari 590