Musnad Ahmad 962:105

Zayd ibn al-Hubab narrated to us, Mu'awiyah ibn Salih narrated to me, al-Safar ibn Nusayr al-Azdi narrated to me, from Yazid ibn Shurayh al-Hadrami, from Abu Umamah, from the Prophet (peace and blessings of Allah be upon him) that he said: "None of you should come to the prayer while he is suppressing the urge to urinate. And none of you should lead others in prayer and single himself out with supplication to the exclusion of them; for whoever does that has betrayed them."