Allah Almighty says: "And they were not commanded except to worship Allah, making the religion sincerely His, inclining to the truth, and to establish prayer and give zakah; and that is the upright religion." [Surah al-Bayyinah: 5]
(7221) Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that he (peace and blessings be upon him) said: "Islam is built upon five pillars: (1) bearing witness that there is no god but Allah and that Muhammad (peace and blessings be upon him) is the Messenger of Allah, (2) establishing prayer, (3) giving zakah, (4) performing Hajj to the House of Allah, and (5) fasting in Ramadan."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7221