Assalamu ‘alaikum warahmatullahi wabarakatuh,
In the time of Prophet Muhammad until the next hundred of years indeed, Zakat on Earnings is unknown. Even the books of fiqh did not include the chapter of Zakat on Earnings.
Zakat on Earnings is a moslem scholars (ulama) ijtihad today. It comes from a reasonable ijtihad which has a strong principle. It must be remembered that even in the days of the Prophet Muhammad has existed a variety of professions, but in the terms of income, the conditions are different from today.
There is a difference point of view among the ulamas to determine the property that is an obligation of zakat. These are the type of ulama who think about zakat on earnings property :
1. Opponents Argument of Zakat on Earnings
Their principal of zakat is based on their point of view which said that everything that related to zakat is fully related to ubudiyah, so that all forms of rules and conditions should only be performed if there is clear instructions or direct example of the Prophet Muhammad. If ther are no, then no need to invent.
The Ulama which belongs to this view is the Zahiri fuqaha like Ibn Hazm and others and also jumhur moslem scholars. Unless Hanafiyah Mazhab who was giving flexibility criteria to the property that obligate to Zakat.
Generally, The Hijaz and also including Dr. Wahbah Az-Zuhaily are in the opponent side of zakat on earnings, because the ulama shalaf (earlier ulama) before them never criticize about this zakat. And also, generally the classic book of fiqh doesn’t mention the zakat on earnings.
2. Proponents Argument of Zakat on Earnings
Profession in the past has been there, but the social conditions are different from today. According to proponents of zakat on earnings, the essential reference is a someone wealth. According to their analysis, in that moment, the rich people who has the property is still limited such as the traders, farmers and ranchers. It is different from today, where not all traders are rich, the ranchers and the farmers in this country even the average life of poverty.
Conversely, professional people who previously did not produce anything meaningful, but now it is become a profession that made them rich with wealth. Their income exceeds the traders, farmers and ranchers with tens of times even hundreds of times.
This is one of the ulama underlying ideas of ijtihad today to establish a zakat on earnings. The point is the principle of justice. But of course with nothing out of the mainframe itself. The philosophy of zakat is to set aside the property of the rich to the poor.
This social changing is the background of ulama ijtihad today to look back at the way we look in determining: who is rich and who is poor?
The point is to collect wealth of the rich to give to the poor. In ancient times, the rich people identically are the traders, farmers and ranchers. But in this day and age, the rich people are the professionals with high salary. Times change but the principle of zakat has not changed. (Ahmad Sarwat, Lc/rumahfiqih.com)