Tradition

Abu Hamzah al-Thamali (r.a.) reports Imam Muhammad Baqir (a.s.) as saying: Islam is based on five pillars: the observance of prayer, the payment of zakat, pilgrimage to the House, fast during Ramadan and belief in our leadership (Wilayat), the Ahle Bait (a.s.). Four of these have been given allowance, but there is no allowance regarding Wilayat. He who has no money then no zakat is due from him, he who has no money, no pilgrimage is prescribed for him, if one is ill, he can pray sitting and need not observe fasting during Ramadan. As for Wilayat, it is incumbent upon every one whether he is sound or ill, and whether he has or does not have money.
Al-Khesaal chap 5 trad 21