Al-Matalib al-'Aliyah 1846 — The sanctity of a Muslim's blood

It is narrated from Imam al-Zuhri (may Allah have mercy on him) that when al-Hajjaj bin Yusuf besieged Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with him), he arrested a man and handed him over to Salim bin Abdullah bin Umar (may Allah have mercy on him) so that he would kill him. Salim asked the man, "Are you a Muslim?" He replied, "Yes." He asked again, "Have you prayed the morning prayer today?" He said, "Yes." At this Salim said to him, "Go, be on your way; I now have no lawful ground to kill you." When al-Hajjaj learnt of his conduct, he asked, "What became of that man?" Salim replied, "I asked him whether he was a Muslim, and he affirmed it; then I asked whether he had prayed the Fajr prayer, and he said yes. And my father told me this blessed saying of the Messenger of Allah (peace and blessings be upon him): 'Whoever prays the morning prayer is in the protection and security of Allah Almighty until he reaches the morning or the evening.'" Al-Hajjaj said (objecting), "But this man is one of the killers of Sayyiduna Uthman (may Allah be pleased with him)!" Salim answered decisively, "I am not the heir and guardian (wali) of Sayyiduna Uthman, that I should go about taking retaliation from his killers." When this news reached his noble father, Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), he was so overjoyed that he came out quickly, dragging his lower garment, met Salim and, praising this faith-inspiring decision of his, said, "My son! I named you 'Salim' precisely so that you would remain safe (from such trials); I named you Salim so that you would remain safe."
This narration makes clear the great scholarly point that performing the Fajr prayer is a warrant of complete security from Allah for the believer, and discerning jurists always make the Prophetic hadith their shield in times of trial, to avoid shedding blood unjustly.