From the 12th century Parabolae of Odo of Cheriton (no.56):
Contra non implentes uotum.
Mus semel cecidit in spumam uini uel cervisie, quando bul[l]iuit. Catus transiens audiuit Murem pipantem eo quod exire non potuit. Et ait Catus: Quare clamas? Respondit: Quia exire non ualeo. Ait Catus: Quid dabis mihi, si te extraxero? Ait Mus: Quicquid postulaueris? Et ait Catus: Si te hac uice liberauero, uenies ad me cum te uocauero? Et ait Mus: Firmiter hoc promitto. Ait Catus: Iura mihi. Et Mus iurauit. Catus Murem extraxit et ire permisit. Semel Catus esuriuit et uenit ad foramen Muris, et dixit ei quod ad ipsum exiret. Dixit Mus: Non faciam. Ait Catus: Nonne iurasti mihi? Dixit: Frater, ebria fui, quando iuraui.
Sic plerique, quando infirmi uel in carcere uel in periculo, proponunt et promittunt uitam emendare, ieiunare uel huiusmodi. Sed cum periculum euaserunt, uotum implere non curant, dicentes: In periculo fui et ideo non teneor.
Against not filling a vow:
A mouse once fell into a cask of wine or beer while he was drinking from it. A cat happening to pass by heard the mouse squeaking because he was not able to get out.
-And the cat said: Why are you crying?
-He answered: Since I’m not strong enough to get out.
-The cat said: What will you give me if I pull you out?
-The mouse replied: What will you demand?
-And the cat said: If I free you from this plight, will you come to me when I call you?
-And the mouse said: Solemnly do I promise it.
-The cat said: Swear to me.
And the mouse swore to him. The cat pulled out the mouse and allowed him to leave.
Some time later the cat grew hungry and came to the door of the mouse, and said to him that he should come out.
-The mouse said: I will not do it.
-The cat said: Didn’t you swear to me?
-He said: Brother, I was drunk when I swore
Thus many, when sick or in prison or in danger, propose or promise to improve thier life, to fast, or something else. But when they have escaped the danger they have no concern with filling the vow, saying : I was in danger and so I’m not held by it.