The Messenger of Allah ﷺ was more particular about observing the supererogatory rak'ahs before the dawn prayer than about observing any of the other supererogatory prayers. (Using translation from Abū Dāʾūd 1254)   

«لَمْ يَكُنْ رَسُولُ اللهِ ﷺ عَلَى شَيْءٍ مِنَ النَّوَافِلِ أَشَدَّ مُعَاهَدَةً مِنْهُ عَلَى الرَّكْعَتَيْنِ قَبْلَ الْفَجْرِ»  

The Prophet ﷺ never omitted four rak'ahs before the noon prayer, and two rak'ahs before the dawn prayer. (Using translation from Abū Dāʾūd 1253)   

كَانَ رَسُولُ اللهِ ﷺ «لَا يَدَعُ أَرْبَعًا قَبْلَ الظُّهْرِ وَلَا الرَّكْعَتَيْنِ قَبْلَ صَلَاةِ الصُّبْحِ»