The sunnah he never left

No voluntary prayer was kept more regularly than the two rak'ahs before Fajr.

Narrated by Aishah

The Prophet ﷺ was not more regular in any voluntary prayer than he was in the two rak'ahs before Fajr.

Sahih al-Bukhari 1163, Sahih Muslim 724

What this hadith teaches

He kept them even when travelling, which shows how important they are.

Reference and grade

Grade
Sahih: agreed upon by al-Bukhari and Muslim
Narrator
Aishah

The hadith in Arabic نص الحديث

لَمْ يَكُنِ النَّبِيُّ صلى الله عليه وسلم عَلَى شَىْءٍ مِنَ النَّوَافِلِ أَشَدَّ مِنْهُ تَعَاهُدًا عَلَى رَكْعَتَىِ الْفَجْرِ

Arabic text of Sahih al-Bukhari 1163, as given on sunnah.com.