It is narrated from Aisha (may Allah be pleased with her), she said: At first, the prayer was made obligatory as two rak'ahs, then the prayers performed in residence were increased, and the prayer during travel was kept as it was. Zuhri (may Allah have mercy on him) says: I asked, then why did Aisha (may Allah be pleased with her) herself perform the full prayer during travel? Urwah replied: She adopted the same interpretation as Uthman (may Allah be pleased with him).
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 357
Hadith Takhrijأخرجه البخاري: القصر، باب يقصر إذا خرج من موضعه: 1090، 350 - ومسلم: صلاة المسافرين، باب صلاة المسافرين قصرها: 685.