It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "It is not lawful for a man to pray while holding back urine and the like; rather, he should first relieve himself. Nor is it lawful for anyone to lead people in prayer without their permission, nor to single himself out for a supplication. If he does so, he has betrayed them. Nor is it lawful for a man to look through any opening into a house. If he looks, it is as if he has entered the house without permission."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5349