Oh this Bahai Faith keeps on getting better. 1164. Vasectomy to Avoid Having Unwanted Children not Permitted if it Results in Permanent Sterility" Directly to your question about having a vasectomy, in general it is not permissible to have a surgical operation for the purpose of avoiding having unwanted children if such an operation could result in permanent sterility https://bahai-library.com/hornby_lights_guidance_2.html&chapter=2#n1164
