“marriage is by no means an obligation” - 6 February 1973

...Of course, under normal circumstances, every person should consider it his moral duty to marry. And this is what Bahá'u'lláh has encouraged the believers to do. But marriage is by no means an obligation. In the last resort it is for the individual to decide whether he wishes to lead a family life or live in a state of celibacy. 

- Shoghi Effendi  (From a letter to an individual believer, May 3, 1936; cited by the Universal House of Justice, in a letter to an individual believer, February 6, 1973: ‘Messages from the Universal House of Justice, 1968-1973’; compilation: ‘Lights of Guidance’)