بُلُوغُ الْمَرَامِ
Bulugh al-Maram 176
The Book of Prayer
وَعَنْ أَمْ سَلَمَةَ رَضِيَ اَللَّهُ عَنْهَا قَالَتْ: { صَلَّى رَسُولُ اَللَّهِ - صلى الله عليه وسلم -اَلْعَصْرَ, ثُمَّ دَخَلَ بَيْتِي, فَصَلَّى رَكْعَتَيْنِ, فَسَأَلْتُهُ, فَقَالَ: "شُغِلْتُ عَنْ رَكْعَتَيْنِ بَعْدَ اَلظُّهْرِ, فَصَلَّيْتُهُمَا اَلْآنَ", قُلْتُ: أَفَنَقْضِيهِمَا إِذَا فَاتَتْنَا? قَالَ: "لَا" } أَخْرَجَهُ أَحْمَدُ [1] .
Narrated Umm Salamah (RA): Allah's Messenger (ﷺ) came to my house after offering 'Asr prayer and offered two Rak'a, then I asked him about that and he replied, "I was kept busy (and failed to pray) the two (Sunnah) Rak'a after Zuhr prayer, so I offered them now." I asked him, "Should we offer them if we miss them?" He (ﷺ) replied, "No." [Reported by Ahmad].
Sunnah.com reference: Book 2, Hadith 30