Seeking livelihood is obligatory like seeking knowledge; and it is of four kinds. Obligatory: earning the least sufficiency for oneself, one's dependants, and discharging one's debt.
Book of Livelihood and Etiquette — Preface
Seeking livelihood is obligatory like seeking knowledge; and it is of four kinds. Obligatory: earning the least sufficiency for oneself, one's dependants, and discharging one's debt.
Recommended: earning surplus beyond the least sufficiency, in order to assist therewith a poor person, or join kin therewith; and that is better than supererogatory worship.
Permissible: earning surplus beyond that for indulgence and adornment.
Unlawful: earning what is for accumulation and boasting, even though it be from lawful [sources].
The best livelihood is jihād, then trade, then agriculture, then craftsmanship.
Knowledge too is of four kinds: obligatory—and it is learning what one needs to discharge the duties, and know lawful and unlawful in one's own situations.
Recommended: learning surplus beyond what one needs in order to teach it to whoever needs it; and that is better than supererogatory worship.
Permissible: learning surplus beyond that for adornment and completeness.
Unlawful: learning in order to show off thereby among scholars, and dispute thereby with fools.
The scholar must teach another if the latter requests [instruction] of him, until he reaches the first level.
The scholar is not obliged to answer what is asked of him except when he knows that what he was asked about is not known to anyone else.
If an unbeliever asks a Muslim to teach him the Qurʾān and fiqh, there is no harm in that, in hope that he grasp its virtues and become Muslim.