[Ruling on Spending Zakat on Public Interests]

Answer—and Allah is the Granter of success: The jurists of the madhhab have said that it is permissible to spend what remains of the share of combatants (al-mujāhidīn) on public interests; however, they stipulated for this the presence of the Imām and that the poor be sufficiently provided for.
I say: “In the path of Allah (sabīl Allāh)” is one of the eight categories of disbursement. From the words of the jurists of the madhhab it is understood that “in the path of Allah” is a general term under which public interests—such as mosques, watering places, and roads—fall.
On this basis, if there is no Imām in a given time, then the share of “in the path of Allah” is entirely surplus, due to the absence then of combatants; that surplus is to be spent on public interests, provided the poor are sufficiently provided for, since there is no hindrance to that. However, the permissibility of doing so requires a fatwa from a learned scholar for each particular public interest.
It may be that building a mosque in a village is in the public interest, and it may not be—because something else suffices in its place. It may be that expanding a mosque is in the public interest, and it may not be; likewise for repairing watering places and roads. The people of the village may be poor and in need of a mosque—or they may not be. It may be that building a mosque entails a harm—or it may not. For this reason we have said: the permissibility of spending zakat on public interests depends upon a scholar’s fatwa.
If it be said: “In the path of Allah” is a term for jihad alone.
We say: Rather, it also includes whatever brings a general benefit whose advantage returns to the community of Muslims.
The proof for that is that there is no doubt that the Imāms may build prisons, infirmaries, and mosques from the public treasury (Bayt al-Māl) and from zakat; likewise they may assign stipends for judges and the like from the public treasury, and similar public interests. This is how the Commander of the Faithful ʿAlī b. Abī Ṭālib, peace be upon him, and the Imāms from his progeny acted: they did not restrict zakat to jihad alone; rather, they associated with it other matters like those we have mentioned.
Yes: what ought to be reserved to the Imām, to the exclusion of others, is spending zakat on implements of war, mustering armies, building prisons, appointing judges and governors, and the like of what is specific to the Imām. It is not permissible for anyone other than the Imām to spend zakat on any of that, by agreement that such matters belong to the Imāms alone.
As for repairing roads, building infirmaries, mosques, watering places, and the like among public interests that do not require the presence of an Imām to be carried out—there is no impediment to spending zakat on them after the consideration and fatwa of a mujtahid, as mentioned first; without that, it is neither appropriate nor permissible.
It is fitting to mention here that calling to Allah and guiding (people) is the first matter upon which the share of “in the path of Allah” should be spent in a time like this; attention should not be given to other public interests until that is sufficiently provided for—even though all of them are public interests, they nonetheless differ: among them are general religious interests and general worldly interests, and the religious are given precedence over the worldly.
General religious interests are of ranks: foremost among them are jihad, calling to the religion of Allah and guiding, enjoining right and forbidding wrong, and disseminating knowledge—all of these are of one standing.
Thereafter, the remaining public interests are to be arranged according to need, under the supervision and judgment of the mujtahid and in accordance with his fatwa.
If it be said: It follows, according to what you have stated, that zakat should not be disbursed to a poor person except after the scholar’s consideration and fatwa—since poor people differ and vary in their need.
We say: Although the poor differ in their degree of need, they are equal in the validity of placing zakat among them, for they deserve it on account of poverty; and “poverty” is a term that encompasses them all, and it is a clear attribute.
This is unlike public interests: building a given mosque may be a public interest, while building another mosque may not be; likewise for watering places and repairing roads. A microphone (loudspeaker) may be a public interest—if the village is large; and it may not be—if the village is small, or there are microphones in other mosques in the village. And so it is with the rest of public interests.
Hence we have said: zakat may not be spent on public interests except under the fatwa of a learned mujtahid, and according to what his judgment requires in assessing the need of the particular interest.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1