Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
bayhaqi:7705 – Abū al-Ḥasan ʿAlī b. Aḥmad b. ʿAbdān > Aḥmad b. ʿUbayd al-Ṣaffār > Ismāʿīl b. Isḥāq > Sulaymān b. Ḥarb > Ḥammād b. Zayd > Ayyūb > Abū Rajāʾ > Ibn ʿAbbās Yakhṭub > al-Minbar /

[Machine] I heard Ibn Abbas giving a sermon on the pulpit, and he was saying about the charity of Fitr: "A Saa' of food. This is the correct, established position."  

البيهقي:٧٧٠٥ – أَخْبَرَنَا أَبُو الْحَسَنِ عَلِيُّ بْنُ أَحْمَدَ بْنِ عَبْدَانَ أنبأ أَحْمَدُ بْنُ عُبَيْدٍ الصَّفَّارُ ثنا إِسْمَاعِيلُ بْنُ إِسْحَاقَ ثنا سُلَيْمَانُ بْنُ حَرْبٍ ثنا حَمَّادُ بْنُ زَيْدٍ عَنْ أَيُّوبَ قَالَ سَمِعْتُ أَبَا رَجَاءٍ يَقُولُ

سَمِعْتُ ابْنَ عَبَّاسٍ يَخْطُبُ عَلَى الْمِنْبَرِ وَهُوَ يَقُولُ فِي صَدَقَةِ الْفِطْرِ صَاعًا مِنْ طَعَامٍ هَذَا هُوَ الصَّحِيحُ مَوْقُوفٌ  

See similar narrations below:

Collected by Nasāʾī's Kubrá
nasai-kubra:2301 – Qutaybah b. Saʿīd > Ḥammād > Ayyūb > Abū Rajāʾ > Ibn ʿAbbās Yakhṭub > Minbarikum / Minbar al-Baṣrah

[Machine] I heard Ibn Abbas giving a sermon on your pulpit, meaning the pulpit of Basra, saying: The Zakat al-Fitr is "a saa' (measurement) of food."  

الكبرى للنسائي:٢٣٠١ – أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ قَالَ حَدَّثَنَا حَمَّادٌ عَنْ أَيُّوبَ عَنْ أَبِي رَجَاءٍ قَالَ

سَمِعْتُ ابْنَ عَبَّاسٍ يَخْطُبُ عَلَى مِنْبَرِكُمْ يَعْنِي مِنْبَرَ الْبَصْرَةِ يَقُولُ صَدَقَةُ الْفِطْرِ «صَاعٌ مِنْ طَعَامٍ»