Is it possible to atone for a vow and engage in fishing for a livelihood after verifying the halal source of the fish, or is it obligatory to adhere to the vow and seek another source of livelihood?

The Hanbalis held that for a vow concerning a permissible act, the person has the choice between fulfilling it or offering an expiation for an oath. A vow to refrain from dealing with sailors because what they sell is unlawful is invalid and entails nothing, as abstaining from the unlawful is obligatory. We believe that this vow does not bind you to anything. However, if you wish, you may offer an expiation for an oath if you intend to deal with these sailors, based on the madhhab of Imam Ahmad.