something that provides neither milk nor a mount. I offered him a large young she-camel to take, but he refused. Here she is; I have brought her to you, O Messenger of Allah. Take her.’ The Messenger of Allah, may Allah bless him and grant him peace, said to him, ‘That is what you owe, but if you voluntarily offer something better, Allah will reward you for it, and we will accept it from you.’ He replied, ‘Here she is, O Messenger of Allah. I have brought her to you, so take her.’ The Messenger of Allah, may Allah bless him and grant him peace, then ordered that she be accepted and prayed for blessing upon his wealth.”
The ruling indicated by this hadith—that an animal older than the required age suffices—is the position of the great majority of scholars, including the well-known jurists and others. It is thus established that replacing what is obligatory with something better is permissible, indeed recommended, whether the obligation is imposed by Islamic law or undertaken by the person himself. There is no distinction between an obligation owed as a general liability and one attached to a specifically designated thing. Although a general liability is unspecified in one respect, it is nevertheless defined and distinguished from other things. Hence, there is undoubtedly no entitlement to replace it with something inferior.
Accordingly, if someone vows to endow something but endows something better, that is preferable. Thus, if he vows to build for Allah a mosque of a specified description, or to establish an endowment of a specified description, then builds a better mosque and establishes a better endowment, that is preferable.
Even if he specifies the property, saying, ‘I undertake, for Allah’s sake, to make this house into a mosque, or to endow it for the poor and needy,’ then builds something better or endows something better, that is preferable. This is like someone who vows to pray in al-Aqsā Mosque but prays in the Sacred Mosque instead, or someone who owes a one-year-old she-camel but gives something better.
The jurists have disagreed about exceeding a prescribed obligatory amount—for example, giving more than one sā‘ for zakat al-fitr. Most permit it, and this is the position of al-Shāfi‘ī, Abū Hanīfah, and Ahmad