The Forty Hadith of Al-Nawawi.
On the authority of Abu 'Abd al-Rahman 'Abdullah Ibn 'Umar Ibn al-Khattab, may Allah be pleased with them both, who said:
I heard the Messenger of Allah, peace and blessings of Allah be upon him, say:
"Islam has been built upon five [pillars]: testifying that there is no god but Allah
and that Muhammad is His servant and His messenger,
establishing prayer, paying zakat,
performing the pilgrimage to the House, and fasting Ramadan."
It was narrated by al-Bukhari and Muslim.
This hadith demonstrates that Islam is built upon monumental foundations,
without which a Muslim's faith cannot be sound.
The Prophet, peace be upon him, compared Islam to a building
to indicate that these pillars
are the fundamental supports upon which the religion rests;
thus, whenever a Muslim safeguards them,
their faith is strengthened and their religion made upright.