Says the Shaykh Abu Ja'far: Our belief concerning the obligation to obey the law (taklif) is that Allah imposes upon His slaves (mankind) only such legal obligations as are within their power (to obey), for He says:
“Allah tasketh not a soul beyond its capacity” (Qur'an 2:286).
Now (in the Arabic idiom) wus' (capacity, scope) indicates a lesser degree of potentiality than taqa (strength). And (Imam Ja'far) as-Sadiq has said: I swear by Allah, Allah has not burdened His slaves, save to a lesser extent than their capacity.
For He has only imposed upon them five prayers during the course of a day and night; and only thirty days of fast during the year; and only five out of every two hundred dirhams (as zakat); and only one pilgrimage during the course of a lifetime, although the full extent of their capacity is greater.2