Talhah bin Abdullah bin Awf asked Sayyiduna Abu Hurayrah (may Allah be pleased with him) about a garment in which a man has had intercourse, and he said: "If you see filth on the garment and then forget the spot, wash the whole garment; and if you are in doubt, sprinkle water on the garment and pray in it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4104