Al-Hasan said:

Ibn Abbas preached towards the end of Ramadan on the pulpit (in the mosque) of al-Basrah. He said: Bring forth the sadaqah relating to your fast. The people, as it were, could not understand. Which of the people of Medina are present here? Stand for your brethren, and teach them, for they do not know.

The Messenger of Allah ﷺ prescribed this sadaqah as one sa' of dried dates or barley, or half a sa' of wheat payable by every freeman or slave, male or female, young or old. When Ali came (to Basrah), he found that price had come down. He said: Allah has given prosperity to you, so give one sa' of everything (as sadaqah).

The narrator Humayd said: Al-Hasan maintained that the sadaqah at the end of Ramadan was due on a person who fasted.

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا سَهْلُ بْنُ يُوسُفَ، قَالَ حُمَيْدٌ أَخْبَرَنَا عَنِ الْحَسَنِ، قَالَ خَطَبَ ابْنُ عَبَّاسٍ رَحِمَهُ اللَّهُ فِي آخِرِ رَمَضَانَ عَلَى مِنْبَرِ الْبَصْرَةِ فَقَالَ أَخْرِجُوا صَدَقَةَ صَوْمِكُمْ فَكَأَنَّ النَّاسَ لَمْ يَعْلَمُوا فَقَالَ مَنْ هَا هُنَا مِنْ أَهْلِ الْمَدِينَةِ قُومُوا إِلَى إِخْوَانِكُمْ فَعَلِّمُوهُمْ فَإِنَّهُمْ لاَ يَعْلَمُونَ فَرَضَ رَسُولُ اللَّهِ ﷺ هَذِهِ الصَّدَقَةَ صَاعًا مِنْ تَمْرٍ أَوْ شَعِيرٍ أَوْ نِصْفَ صَاعٍ مِنْ قَمْحٍ عَلَى كُلِّ حُرٍّ أَوْ مَمْلُوكٍ ذَكَرٍ أَوْ أُنْثَى صَغِيرٍ أَوْ كَبِيرٍ فَلَمَّا قَدِمَ عَلِيٌّ - رضى الله عنه - رَأَى رُخْصَ السِّعْرِ قَالَ قَدْ أَوْسَعَ اللَّهُ عَلَيْكُمْ فَلَوْ جَعَلْتُمُوهُ صَاعًا مِنْ كُلِّ شَىْءٍ . قَالَ حُمَيْدٌ وَكَانَ الْحَسَنُ يَرَى صَدَقَةَ رَمَضَانَ عَلَى مَنْ صَامَ .