Classical Islamic jurisprudence developed the waqf into a legal device far more specific than a general habit of charitable giving, with fixed rules on how a founder could settle an asset, name an administrator and specify beneficiaries in a deed that later generations of jurists could not simply overrule. Scholars have long debated whether the institution influenced the charitable trust that later developed in English law, a claim made on the strength of contact during the Crusades and Norman Sicily, though the connection remains contested rather than settled.
What is not contested is the scale the institution reached under later Muslim empires. Ottoman sultans and their officials used a single waqf deed to fund an entire complex at once, not just a mosque but an attached madrasa, a soup kitchen, a hospital and a library, all supported from the rents of shops and farmland the founder had assigned to the endowment in perpetuity. Suleiman the Magnificent's sixteenth century Suleymaniye complex in Istanbul is the clearest surviving example of this model: one endowment, drafted once, still generating the income that built and sustained an entire institutional quarter of the city around a single mosque.