There is no direct clear cut evidence for sadaqatul fitr in thr quran, but there is an indication towards it. Evidence of sadaqatul fitr, the following evidences comes together to make fitrana wajib:
- Sunan abi dawood:1622
- Surah a’la
Fitrana is wajib Zakat is fard
However, the people that we give both to, are eligible for both. Fitrana was made wajib before zakat and it was two days before eid ul fitr.
The three other imams say that fitrana is fard but denying it is not kufr.
The one who must give it, is one is above nisab, however even if one is below the nisab but has the means such as a home, they must give when they do have a home.
One doesnt have to pay for his slave, or wife, or children, but if he does, it is okay.
For any assets for business, you dont have to give fitrana based on it as you are already paying zakat on it.