‘Abdallah b. Mas'ud said: I cannot count how often I heard God’s Messenger reciting in the two rak'as after the sunset prayer and in the two rak'as before the dawn prayer, “Say, O unbelievers,” and “Say, He is God, one God.” Tirmidhi transmitted it, and Ibn Majah transmitted it on Abu Huraira’s authority, but he did not mention “after the sunset prayer.”
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَبْدُ اللَّهِ بْنِ مَسْعُودٍ قَالَ: مَا أحصي مَا سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقْرَأُ فِي الرَّكْعَتَيْنِ بَعْدَ الْمَغْرِبِ وَفِي الرَّكْعَتَيْنِ قَبْلَ صَلَاةِ الْفَجْرِ: بِ (قُلْ يَا أَيُّهَا الْكَافِرُونَ) و (قل هوا لله أحد) رَوَاهُ التِّرْمِذِيّ وَرَوَاهُ ابْنُ مَاجَهْ عَنْ أَبِي هُرَيْرَةَ إِلَّا أَنه لم يذكر: «بعد الْمغرب»
sunnah.com