Musnad Ahmad 535:7

Yahya ibn Ishaq narrated to us, he said: Ibn Lahi'ah narrated to us, from Ubayd Allah ibn al-Mughirah, he said: Abdullah ibn al-Harith ibn Juz' al-Zubaydi informed me, he said: I saw the Messenger of Allah (may Allah bless him and grant him peace) urinating while facing the Qibla. And I am the first person to have told the people about that.