The Messenger of Allah ﷺ taught me to say when the adhan for the sunset prayer was called; "O Allah, this is the time when Thy night comes on, Thy day retires, and the voices of Thy summoners are heard, so forgive me."  

عَلَّمَنِي رَسُولُ اللَّهِ ﷺ أَنْ أَقُولَ عِنْدَ أَذَانِ الْمَغْرِبِ اللَّهُمَّ إِنَّ هَذَا إِقْبَالُ لَيْلِكَ وَإِدْبَارُ نَهَارِكَ وَأَصْوَاتُ دُعَاتِكَ فَاغْفِرْ لِي  

The Messenger of Allah ﷺ taught me to say when the adhan for the sunset prayer was called; "O Allah, this is the time when Thy night comes on, Thy day retires, and the voices of Thy summoners are heard, so forgive me." (Using translation from Abū Dāʾūd 530)  

عَلَّمَنِي رَسُولُ اللَّهِ ﷺ أَنْ أَقُولَ عِنْدَ آذَانِ الْمَغْرِبِ «اللَّهُمَّ هَذَا إِقْبَالُ لَيْلِكَ وَإِدْبَارُ نَهَارِكَ وَأَصْوَاتُ دُعَاتِكَ فَاغْفِرْ لِي»  

[Machine] "To me, messenger of Allah ﷺ , my saying upon the call to the evening prayer: O Allah, at the coming of Your night and the departure of Your day, and the voices of Your supplications, and the presence of Your prayers, forgive me. And whenever the night falls, she used to say: My Lord, forgive, have mercy, and guide to the straight path."  

لِي رَسُولُ اللهِ ﷺ قُولِي عِنْدَ أَذَانِ الْمَغْرِبِ اللهُمَّ عِنْدَ إِقْبَالِ لَيْلِكَ وَإِدْبَارِ نَهَارِكَ وَأَصْوَاتِ دُعَائِكَ وَحُضُورِ صَلَوَاتِكَ اغْفِرْ لِي وَكَانَتْ إِذَا تَعَارَتْ مِنَ اللَّيْلِ تَقُولُ رَبِّ اغْفِرْ وَارْحَمْ وَاهْدِ السَّبِيلَ الْأَقْوَمَ  

"اللَّهُمَّ هَذَا إِقْبَالُ لَيلكَ وَإدْبَارُ نَهَاركَ وأصْواتُ دُعَائكَ، فَاغْفر لِي".