Tawoos narrates that a man asked Sayyiduna Ibn Umar (may Allah be pleased with them) why he no longer participates in jihad. He replied: "I heard the Noble Prophet (peace and blessings be upon him) say that Islam is built upon five things: bearing witness that there is no deity except Allah, establishing prayer, giving zakat, performing Hajj of the House of Allah, and fasting in Ramadan."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6301