A prisoner, showing sincere faith in the Cause, may be accepted as a Bahá’í on the same basis of investigating his qualifications as to belief as any other individual outside prison. Each case should be carefully considered on its own merits. Naturally, a person in confinement cannot be active in any community and administrative work. When he gets out, he becomes part of the community in which he resides. No new ruling is required in this matter. All other details in relation to prisoners can be decided by the National Spiritual Assembly concerned as they arise.

Shoghi Effendi, The Unfolding Destiny of the British Bahá’í Community, p. 352

There is no reason why a prisoner should not be accepted as a declared believer on the same basis as anybody else. They are now expiating their crime against society, and, if their hearts have changed, and they accept the Cause, there is no reason why they should be excluded from membership.

Shoghi Effendi, Lights of Guidance, no. 251

You have already, through at last facing yourself and acknowledging that you have both failed and erred in managing your life so far, set your feet on the right path. But now this new and spiritual condition in you is going to be proved - and the proving, the testing, will surely consist of the way you determine to take your punishment. Life is based on laws: physical, man-made, and spiritual. As you have broken the laws of the society in which you live, you will have to stand up like a man and take your punishment. The spirit in which you do this is the most important thing, and constitutes a great opportunity for you . . . at present, until your sentence is up, you must live within yourself in a way not to spoil the new future awaiting you. You must not become bitter - for after all you are only reaping what you planted. Bahá’u’lláh and ‘Abdu’l-Bahá through no crime of their own, spent the better part of their lives in exile and imprisoned, but they never became embittered although they were the victims of injustice. You, on the other hand, are the victim of injustice which you have inflicted on yourself - therefore you certainly have no right to be bitter towards the world. He urges you to grasp firmly the teachings of our Faith, the love of your family and many Bahá’í friends, to put the past behind entirely, realizing that it can do you no more harm; on the contrary, through changing you and making you spiritually aware, this very past can be a means of enriching your life in the future!

Shoghi Effendi, Unfolding Destiny, pp. 449-450

[T]hose who accept Bahá’u’lláh under these conditions [imprisonment] cannot undertake administrative responsibilities, nor can Local Assemblies be formed in prisons.

Universal House of Justice, Lights of Guidance, no. 25

[Y]ou instance the difficulties of local communities which are faced with the task of reorienting and integrating into the Cause new believers who enter with all sorts of immoral and even criminal tendencies from their former life. This is indeed difficult, but this is the very stuff of the work of the Cause. The Bahá’í Faith not only provides teachings in accordance with which the behavior of human beings can be reformed, but also makes available a spiritual power which reinforces the devoted efforts of every believer, whether veteran or neophyte. Arising to serve the Cause has, itself, a transforming effect upon believers, as the beloved Guardian wrote with respect to service upon Spiritual Assemblies: "If we but turn our gaze to the high qualifications of the members of Bahá’í Assemblies, as enumerated in ‘Abdu’l-Bahá's Tablets, we are filled with feelings of unworthiness and dismay, and would feel truly disheartened but for the comforting thought that if we arise to play nobly our part every deficiency in our lives will be more than compensated by the all-conquering spirit of His grace and power." Thus, what is most imperative for the promotion of the spiritual life of local Bahá’í communities is the stimulation of the believers to increase their devotion to Bahá’u’lláh, their absolute reliance upon Him and upon His love, and their determination to apply His teachings in every aspect of their lives. This stimulation can be conveyed from heart to heart and mind to mind by devoted Bahá’ís without the need of formal training.

Universal House of Justice, Messages from the Universal House of Justice, 1963-1986, p. 349

Bahá’ís serving prison sentences may participate in Bahá’í activities permitted by prison policies and their personal circumstances. They are encouraged to observe the laws applicable between the individual and God to the extent their circumstances allow. As with other believers, they are free to teach the Faith and, if prison policy allows, hold Bahá’í activities such as firesides, study circles and devotional gatherings within the prison.

USA- NSA, Guidelines for Local Spiritual Assemblies, Chapter 14, p. 37