In the answer to question no. 2182 we stated that the one who does not pray is a kaafir, whether he does not pray out of carelessness and laziness or because he denies it is obligatory.
If Allah guides a person (to Islam) before sunset on the last day of Ramadan, he has to pay zakaat al-fitr, regardless of whether he caught up with the fast or not, because of the hadeeth of Ibn ‘Umar (may Allah be pleased with him) who said: The Messenger of Allah (blessings and peace of Allah be upon him) enjoined the sadaqah of Ramadan upon the people, a saa‘ of dates or a saa‘ of barley, upon every person, free or slave, male or female, among the Muslims.
Narrated by al-Bukhaari, 1503; Muslim, 984.
The words “among the Muslims” are general in meaning and include everyone who became Muslim before sunset on the last day of Ramadan, even if he did not fast.
Ibn Qudaamah (may Allah have mercy on him) said: … With regard to the time when it becomes obligatory, it is when the Sun sets on the last day of Ramadan. It becomes obligatory with the setting of the sun on the last day of the month of Ramadan, so whoever becomes Muslim before sunset has to pay zakaat al-fitr, but if he became Muslim after sunset, he is not obliged to pay it. … al-Layth, Abu Thawr and ashaab al-ra’y said: It becomes obligatory when dawn breaks on the day of Eid, and this was also narrated from Maalik, because it is an act of worship that has to do with Eid, so it does not become obligatory before the day of Eid.
End quote from al-Mughni, 2/358
Al-Nawawi (may Allah have mercy on him) said: The correct view in our opinion is that it becomes obligatory when the sun sets on the night before Eid al-Fitr. This was the view of al-Thawri, Ahmad and Ishaaq, and is mentioned in one report from Maalik. Abu Haneefah and his companions, Abu Thawr, Dawood and another reported that Maalik said that it becomes obligatory when dawn breaks.
End quote from al-Majmoo‘, 6/88. See also Haashiyat al-‘Adawi, 1/515
If he became Muslim after sunset on the last day of Ramadan, then he does not have to pay zakaat al-fitr, because the month has ended, except in the opinion of those who say that it becomes obligatory when dawn breaks. The more correct view is that of the majority of scholars, because of the words of Ibn ‘Umar (may Allah be pleased with him): The Messenger of Allah (blessings and peace of Allah be upon him) enjoined zakaat al-fitr after Ramadan. Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: The end of the fast of Ramadan comes when the sun sets on the night before Eid al-Fitr.
End quote from al-Sharh al-Mumti‘, 6/56.