Fajr prayer
Abu Hurairah narrated at the time of the Fajr prayer the Prophet asked Bilal ibn al-Harith, "Tell me of the best deed you did after embracing Islam, for I heard your footsteps in front of me in Paradise." Bilal replied, "I did not do anything worth mentioning except that whenever I performed ablution during the day or night, I prayed after that ablution as much as was written for me." Ibn Hajar al-Asqalani says in "Fath al-Bari" that "the hadith shows it is permissible to use personal reasoning (ijtihad) in choosing times for acts of worship, for Bilal reached the conclusion he mentioned by his own inference and the Prophet (Allah bless him and give him peace) confirmed him therein." Similar to this, Khubyab bin Adi asked to pray two rakas before being executed by idolators in Mecca, and was hence the first to establish the "sunna" of two rak'as for those who are steadfast in going to their death.