Musannaf Ibn Abi Shayba 3:3536

5913. Abd al-A’la narrated to us, from Burd, from Makhul, that he used to say: If a man has a nosebleed during his prayer, he should depart, perform ablution, then return and build upon what has passed, provided he has not spoken, if he wishes. If he breaks his ablution, he must repeat the ablution and repeat the prayer.