Sahih Bukhari – Hadith No : 1090

Narrated `Aisha: “When the prayers were first enjoined they were of two rak`at each. Later the prayer in a journey was kept as it was but the prayers for non-travelers were completed.” Az-Zuhri said, “I asked `Urwa what made Aisha pray the full prayers (in journey).” He replied, “She did the same as `Uthman did.”

Hadith In Arabic Text :

حدثنا عبد الله بن محمد، قال حدثنا سفيان، عن الزهري، عن عروة، عن عائشة رضى الله عنها قالت الصلاة أول ما فرضت ركعتين فأقرت صلاة السفر، وأتمت صلاة الحضر‏.‏ قال الزهري فقلت لعروة ما بال عائشة تتم قال تأولت ما تأول عثمان‏.‏

Chapter : Shortening the Prayers (At-Taqseer) – كتاب التقصير