It is narrated from Sa'id bin Jubayr (may Allah have mercy on him) that a man came to Ibn Abbas (may Allah be pleased with them both) and said: I find wetness when I stand up to pray.
Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Sprinkle water from a cup, and when you find any of that, consider that it is from it (that is, from the water you sprinkled). The man went away and stayed as long as Allah willed, then came to him after some time. He stated that what he used to feel had gone.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 758