(a) Yahya bin Yazid al-Huna'i says: I asked Anas bin Malik (may Allah be pleased with him) about shortening the prayer; I used to go to Kufah and kept praying two rak'ahs until I returned. Anas (may Allah be pleased with him) said: "When the Prophet (peace and blessings be upon him) set out on a journey of three miles or three farsakhs, he would shorten the prayer" (Shu'bah was in doubt).
(b) In the narration of Abu Dawud: he would pray two rak'ahs; but he did not mention the words 'And I used to go out to Kufah and pray two rak'ahs'.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5446