Hammam bin Munabbih heard Sayyiduna Abu Hurayrah (may Allah be pleased with him) say that the Messenger of Allah (peace and blessings be upon him) said: "The prayer of one who has lost his ablution is not accepted until he performs ablution." A man from Hadramawt asked: What is 'al-hadath' (loss of ablution)? Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: "When wind is passed, with a sound or without a sound."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 569