Hadith 500790
Chapter 2: Purity - كتاب الطهارة
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ عَبَّاسٍ، كَانَ يَرْعُفُ فَيَخْرُجُ فَيَغْسِلُ الدَّمَ عَنْهُ ثُمَّ يَرْجِعُ فَيَبْنِي عَلَى مَا قَدْ صَلَّى .
Yahya related to me from Malik from Nafi that Abdullah ibn Abbas used to have nose-bleeds and would leave to wash off the blood. He would then return and complete his prayer.
Reference Muwatta Malik 500790
USC-MSA web (English) reference : Book 2, Hadith 49