Sahih Muslim Book 4, Hadith Number 1460.

Chapter : Compensation of the missed prayer and excellence of observing it promptly.

‘Aisha reported: The prayer was prescribed as consisting of two rak’ahs, the prayer in travelling remained the same, but the prayer at the place of residence was completed. (Zuhri said he asked ‘Urwa why ‘Aisha said prayer in the complete form during journey, and he replied that she interpreted the matter herself as ‘Uthman did.)