What constitutes the 'excessive' (fahish) amount of non-outlet outflow that invalidates ablution?
Chapter on What Nullifies Purification
Al-Mughni
Book of Purification
Primary text
The apparent position of Ahmad is that there is no fixed limit for the excessive amount that invalidates ablution, other than it being 'excessive' in the heart/mind. When asked for the measure of 'excessive,' he referred to Ibn 'Abbas's statement: 'That which is excessive in your heart.' Another reported measure attributed to him suggests it is the amount one can lift with five fingers of pus, mucus, or vomit, for which there is no issue, but ten fingers was considered much. The established position is that it is measured according to what every person finds excessive within themselves. This standard aligns with Ibn 'Abbas, considering what is deemed excessive by average people, not the overly cautious or the extremely lax.
Supporting text
It was also related that he was asked about the quantity of the excessive amount and replied: 'A span by a span,' and in another instance, 'The amount of a palm-full is excessive.' It was also stated that the excessive amount is that which obligates ablution and is the measure carried away by the five fingers of pus, mucus, or vomit.