It was narrated from Abu Salamah that he asked 'Aishah about the two prostrations (Rak'ahs) that the Messenger of Allah (ﷺ) used to pray after 'Asr. She said:
"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." (TR)
English reference (TR): Vol. 1, Book 6, Hadith 579 (TR)
Arabic reference (TR): Book 6, Hadith 585 (TR)