إِنْ يَخْرُجْ وَأَنَا فِيكُمْ فَأَنَا حَجِيجُهُ دُونَكُمْ
وَإِنْ يَخْرُجْ وَلَسْتُ فِيكُمْ
فَامْرُؤٌ حَجِيجُ نَفْسِهِ وَاللَّهُ خَلِيفَتِي عَلَى كُلِّ مُسْلِمٍ
If he comes forth while I am among you, I shall contend with him on your behalf, but if he comes forth while I am not amongst you, a man must contend on his own behalf and Allah would take care of every Muslim on my behalf (and safeguard him against his evil).
Reference : Sahih Muslim 2937 a
In-book reference : Book 54, Hadith 136
USC-MSA web (English) reference : Book 41, Hadith 7015