Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) said: "Do not face the qiblah or turn your backs to it when relieving yourselves or urinating." And on another occasion he narrated it as marfu' (attributed) to the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 428