Sunan an-Nasa'i, Volume 3, Book 23, Hadith 2517 (DarusSalam) ⓘ

It was narrated from Al-Hasan that Ibn 'Abbas delivered a Khutbah in Al-Basrah and said: "Give Zakah of your fast." The people started looking at one another. So he said: "Whoever is here of the people of Al-Madinah, get up and teach your brothers, for they do not know that the Messenger of Allah has enjoined Salaqatul Fitr upon young and old, free and slave, male and female; half a Sa' of wheat or a Sa' of dates or barely." Al_Hasan said: 'If Allah has given you more, then give more generously of wheat or something else."'

أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ هَارُونَ، قَالَ حَدَّثَنَا حُمَيْدٌ، عَنِ الْحَسَنِ، أَنَّ ابْنَ عَبَّاسٍ، خَطَبَ بِالْبَصْرَةِ فَقَالَ أَدُّوا زَكَاةَ صَوْمِكُمْ ‏.‏ فَجَعَلَ النَّاسُ يَنْظُرُ بَعْضُهُمْ إِلَى بَعْضٍ فَقَالَ مَنْ هَا هُنَا مِنْ أَهْلِ الْمَدِينَةِ قُومُوا إِلَى إِخْوَانِكُمْ فَعَلِّمُوهُمْ فَإِنَّهُمْ لاَ يَعْلَمُونَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم فَرَضَ صَدَقَةَ الْفِطْرِ عَلَى الصَّغِيرِ وَالْكَبِيرِ وَالْحُرِّ وَالْعَبْدِ وَالذَّكَرِ وَالأُنْثَى نِصْفَ صَاعِ بُرٍّ أَوْ صَاعًا مِنْ تَمْرٍ أَوْ شَعِيرٍ ‏.‏ قَالَ الْحَسَنُ فَقَالَ عَلِيٌّ أَمَّا إِذَا أَوْسَعَ اللَّهُ فَأَوْسِعُوا أَعْطُوا صَاعًا مِنْ بُرٍّ أَوْ غَيْرِهِ ‏.‏