Sunan an-Nasa'i #578 · The Book of the Times (of Prayer)

Sunan an-Nasa'iIt was narrated from Abu Salamah that he asked 'Aishah about the two prostrations
Sunan an-Nasa'i · Book 6 · The Book of the Times (of Prayer)
Sunan an-Nasa'i · كتاب 6 · كتاب مواقيت الصلاة
"He used to pray them before 'Asr, but if he got distracted or forgot them, he would pray them after 'Asr, and if he did a prayer he would be constant in it
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي حَرْمَلَةَ، عَنْ أَبِي سَلَمَةَ، أَنَّهُ سَأَلَ عَائِشَةَ عَنِ السَّجْدَتَيْنِ اللَّتَيْنِ، كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّيهِمَا بَعْدَ الْعَصْرِ فَقَالَتْ إِنَّهُ كَانَ يُصَلِّيهِمَا قَبْلَ الْعَصْرِ ثُمَّ إِنَّهُ شُغِلَ عَنْهُمَا أَوْ نَسِيَهُمَا فَصَلاَّهُمَا بَعْدَ الْعَصْرِ وَكَانَ إِذَا صَلَّى صَلاَةً أَثْبَتَهَا ‏.‏
Reference : Sunan an-Nasa'i 578In-book reference : Book 6, Hadith 85