Is it wajib (obligatory) for a person who is not able to fast in Ramadan to give zakat al fitr?

Is it wajib (obligatory) to give sadaqah-al fitr for the people who are not able to fast because of some excuses in Ramadan?

Giving sadaqah al-fitr (voluntary charity) is wajib (obligatory) for a person who can't fast in Ramadan because of an excuse. Such as illness, being a  passenger and being weak and old.. (Omar Nasuhi Bilmen)

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