Mishkat al-Masabih, hadith 782

وَعَنْ جَابِرِ بْنِ سَمُرَةَ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقْرَأُ فِي الْفَجْرِ ب (ق وَالْقُرْآن الْمجِيد) وَنَحْوِهَا وَكَانَتْ صَلَاتُهُ بَعْدُ تَخْفِيفًا. رَوَاهُ مُسْلِمٌ

Jabir b. Samura said that the. Prophet used to recite at the dawn prayer, "Qaf. By the glorious Qur'an"* and a passage of similar length, and his prayer afterwards was shortened. *Al-Qur’an; 50. Muslim transmitted it.