Salim bin Abdullah (may Allah have mercy on him) said: I was with Abdullah bin Umar (may Allah be pleased with them both) on a journey. I saw him, after the sun had risen, perform ablution and then pray. I asked: What prayer is this that you have prayed? He said: After I had performed ablution for the dawn prayer, I touched my private part and forgot (to perform ablution again); so now I have performed ablution and repeated my prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 631