It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that a man asked the Messenger of Allah (peace and blessings be upon him) for permission to wander as an ascetic (abandoning the world), and he (peace and blessings be upon him) said: "The wandering of my Ummah is jihad in the path of Allah, the Mighty and Majestic."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7729