It was narrated from Fatimah bint Abi Hubaish that she suffered from Istihadah and the Messenger of Allah (ﷺ) said to her:
"If it is menstrual blood then it is blood that is black and recognizable, so stop praying, and if it is other than that then perform Wudu', for it is just a vein." (DE)
English reference (DE): Vol. 1, Book 1, Hadith 216 (DE)
Arabic reference (DE): Book 1, Hadith 217 (DE)