Rabi'ah bin Abi Abd al-Rahman (may Allah have mercy on him) says that a man from Iraq came to Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) and said: I have come to you about a matter that has neither head nor tail. Sayyiduna Umar (may Allah be pleased with him) asked: What is it? He said: False testimony has appeared in our land. He said: Has that really happened? He said: Yes. Sayyiduna Umar (may Allah be pleased with him) said: No, by Allah! No man in Islam shall be imprisoned except on the testimony of just witnesses.
Abu Ubayd said: 'La yu'sar' means he shall not be imprisoned.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20631