He—may Allah have mercy on him—was asked:

About leasing buffaloes: someone leases them for one year on unrestricted terms, intending to obtain their milk, and uses them for that purpose. The lease is left unrestricted on the understanding that he will make use of them, though the milk is his aim. Is it also permissible to lease sheep for their milk? And is it permissible to entrust them to someone who will tend them in return for their wool and milk, or not?

He answered:

Praise be to Allah. There is a well-known disagreement on this issue among the early generations and the scholars. The same applies to purchasing a specified quantity of milk over a period, to be received in instalments from these livestock. Prohibition is the well-known position in the schools of Abū Hanīfah, al-Shāfiʿī and Ahmad.

These scholars said:

This is the sale of something neither seen nor described; indeed, it is the sale of something nonexistent that has not yet come into being. A lease concerns benefits, not tangible property, whereas these are tangible things.

These scholars also said:

Hiring a wet nurse to breastfeed is contrary to legal analogy but was permitted because of need. They disagreed about this hiring arrangement.

One view is:

The subject of the contract is her service, while breastfeeding is incidental to it. This is the view of Ibn ʿAqīl and others.

Another view is:

Rather,