It is narrated from Hazrat Asma that during the blessed era of the Prophet (peace be upon him), we used to give two mudd of wheat as Sadaqat-ul-Fitr, according to the same mudd measurement with which you measure.
Hadith Referenceمسند احمد / مسند النساء / 26936
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد حسن