‘He should work with his own hands, benefiting himself and giving in charity.’
They asked, ‘What if he cannot?’ He replied, ‘He should assist a craftsman or do the work for someone who lacks the skill.’
They asked, ‘What if he cannot?’ He replied, ‘He should restrain himself from evil, for that is charity he gives to himself.’”

What further clarifies this matter is that Allah, glorified and exalted, created things in genera, classes and species, sharing certain features while differing from one another in others. Animals, for example, share the capacity for sensation and voluntary movement; these are inseparable characteristics of them all. Hence the Prophet, may Allah bless him and grant him peace, said:

“The truest names are Hārith and Hammām.”

For every person necessarily engages in labour—his earning and work—and necessarily has an intention, which is the starting point of his will. Animals are distinguished from one another by features that set each apart from the others. These distinguishing characteristics are particular to each kind, just as their shared attributes are common to them all. Examples include human speech, the neighing of horses, the grunting of camels, the braying of donkeys, and the like.

Likewise, plants share with animals the characteristics of growth and nourishment. Plants, however, have neither sensation nor a will by which they move. Minerals also share some of these characteristics.

It is known that these classes—which are called species and are distinguished from one another by these particular characteristics—once constituted by these specific distinguishing properties, cannot be turned by any human being into other species. Nor can a human being produce that distinguishing property and invest them with another. Thus, he cannot turn wheat into barley, nor