Is marriage a condition for completing one's faith, and has he who does not marry departed from the Muhammadan Ummah?

Marriage is recommended for those who are able to undertake it, due to its benefits of lowering the gaze, preserving chastity, following the traditions of the Prophets, hoping for righteous offspring, and other virtues. Abstaining from marriage is contrary to what is preferable for one who does not fear committing adultery. However, if one fears it, then abstaining from marriage in such a case constitutes a sin, though it does not reach the level of disbelief.