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»