´It was narrated that Ibn 'Abbas said:` "Allah, the Mighty and Sublime, enjoined the prayer on the tongue of your Prophet (ﷺ): While a resident four (rak'ahs), while traveling two, and at times of fear one."
Hadith Referenceسنن نسائي / كتاب تقصير الصلاة فى السفر / 1443
´It was narrated from Al-Ju'aid:` "I heard As-Sa'ib bin Yazid say: 'During the time of Allah's messenger, the Sa' was equal to a Mudd and third of the Mudd you use today, and the Sa' of today has become large."' (Sahih) Abu 'Abdur-Rahman (An-Nasa'i) said: And Ziyad bin Ayyub narrated it to me.
Hadith Referenceسنن نسائي / كتاب الزكاة / 2521
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:ضعيف، 2/ إسناده ضعيف، الثوري عنعن فى حديث: ’’المكيال مكيال أهل المدينة‘‘ ابو داود (3340) وانظر الحديث الآتي (4598) انوار الصحيفه، صفحه نمبر 341