He made divorce conditional upon something, then he forgot what it was

If someone makes
divorce conditional upon something, such as if he says: “If you visit
So-and-so, then you are divorced,” then divorce takes place when the
condition stipulated is fulfilled, according to the view of the majority of
fuqaha’.

Some of the
scholars are of the view that if he intended thereby to threaten her, urge
her to do something or prevent her from doing something, then it comes under
the heading of an oath (yameen), for which expiation (kafaarah) is required.
This is the view favoured by Shaykh al-Islam Ibn Taymiyah and a number of
other scholars, and it is the basis for fatwas on this website.

Based on that,
if your husband said that he did not remember the action stipulated, but he
did not intend to issue a divorce – rather he merely intended to prevent you
from doing something – then he should offer expiation for his oath, so as to
be on the safe side.

If he says that
he did intend to issue a divorce, but he forgot what the condition was, then
there is no blame on you for doing whatever you want of permissible things,
and no divorce will take place, because the basic principle is that the
marriage remains valid, and no divorce occurs when there is doubt.

Al-Majd Ibn
Taymiyah (may Allah have mercy on him) said in al-Muharrar (2/60): If
there is any doubt concerning divorce or the conditions stipulated for it to
occur, then what matters is the certainty that the marriage remains valid.
End quote.

al-Baghawi (may
Allah have mercy on him) said in at-Tahdheeb (6/104): If a man is
uncertain as to whether he has actually divorced his wife, he should assume
that it has not happened, because the basic principle is that the marriage
remains valid. The same applies if he is uncertain about the number of
divorces: he should assume that it is the lower number, because that is what
is certain. End quote.

And Allah knows
best.