أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا يَزِيدُ، - وَهُوَ ابْنُ هَارُونَ - قَالَ أَنْبَأَنَا 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 أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم فَرَضَ صَدَقَةَ الْفِطْرِ عَلَى الصَّغِيرِ وَالْكَبِيرِ وَالْحُرِّ وَالْعَبْدِ وَالذَّكَرِ وَالأُنْثَى نِصْفَ صَاعٍ مِنْ بُرٍّ أَوْ صَاعًا مِنْ تَمْرٍ أَوْ شَعِيرٍ ‏.‏

It was narrated from Al-Hasan that : Ibn 'Abbas gave a Khutbah in Al-Basrah and said: "Pay the zakah of your fasting." The people started looking at one another. He said: "Whoever there is here from the people of Al-Madinah, get up and teach your brothers, for they do not know that the Messenger of Allah (PBUH) enjoined sadaqat al-fitr on the young and the old, the free and the slave, the male and the female; half a sa' of wheat or a sa' of dried dates or barley.'" Translation Not Available

Book reference: Sunan An Nisai Book 19 Hadith 1580
Web reference: Sunan An Nisai Volume 2 Book 19 Hadith 1581