Imam Malik (may Allah have mercy on him) narrates that it reached him that whenever Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) had a nosebleed, he would leave the prayer, wash off the blood, come back and continue on the same prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3388