I say, and with God's success: The ablution is not invalidated; because it is a condition for anything that exits from outside the two passages to be considered as invalidating the ablution: that it be impure, and that it flows to a place that must be purified, whether in ablution or washing. Here, the two conditions are not met, for although blood is impure, it did not flow to a place that must be purified, and what does not flow is considered to be present but not exiting, thus it does not invalidate the ablution. This is unlike if it were to exceed, as that would invalidate the ablution whether it exits by itself or is expelled by squeezing or otherwise. This is the view of Al-Sarakhsi in his "Al-Jami'", and the author of "Al-Kafi" and "Ghayat Al-Bayan" and "Al-Nihaya", and it was chosen by the author of "Al-Fatawa Al-Bazzaziyya" 4: 12, and it was affirmed by Ibn Al-Humam in "Al-Qadeer" 1: 48, and Al-Laknawi in "Umdah Al-Qari" 1: 70, and God knows best.