Hadith: The Prophet (may Allah's peace and blessings be upon him) did not observe a voluntary prayer more regularly than the two Rak‘ahs of Fajr.

عن عائشةَ أمِّ المؤْمنِين رضي الله عنها قالت:
لَمْ يَكُنِ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ عَلَى شَيْءٍ مِنَ النَّوَافِلِ أَشَدَّ مِنْهُ تَعَاهُدًا عَلَى رَكْعَتَيِ الفَجْرِ.
[صحيح] - [متفق عليه] - [صحيح البخاري: 1169]

‘Ā’ishah, the Mother of the Believers (may Allah be pleased with her), reported:
The Prophet (may Allah's peace and blessings be upon him) did not observe a voluntary prayer more regularly than the two Rak‘ahs of Fajr.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 1169]

Explanation

The Mother of the Believers, ‘Ā’ishah (may Allah be pleased with her), reported that the Prophet (may Allah's peace and blessings be upon him) was never more consistent, diligent, and careful in performing any voluntary prayer than he was with the two Sunnah Rak‘ahs before the Fajr prayer.

Benefits from the Hadith

1. Voluntary prayers refer to all prayers beyond the obligatory ones. Here, it specifically means the regular Sunnah prayers associated with the obligatory prayers.
2. The regular Sunnah prayers are: two Rak‘ahs before Fajr, four Rak‘ahs before Zhuhr and two after it, two Rak‘ahs after Maghrib, and two Rak‘ahs after ‘Ishā’.
3. The regular Sunnah prayer before Fajr is to be prayed both in residence and during travel, unlike the Sunnah prayers for Zhuhr, Maghrib, and ‘Ishā’, which are only prayed when resident.
4. The two Sunnah Rak‘ahs before Fajr are strongly recommended, and they should not be neglected.