What is the ruling on saying: "Let it be well," "I did what I had to do and the rest is up to Allah," or "May Allah make it beautiful," and what is the extent of the authenticity of the saying: "Marriage completes half of one's faith," and does it mean that an unmarried person has not completed their faith?

There is no harm in saying: "The rest is up to Allah" (Al-Baqi 'ala Allah) and "May Allah adorn it" (Allah yuzayyinuha). As for the phrase "Let it be well-being" (khalliha 'awafi), if it is intended as a prayer for well-being or a request for forgiveness, then there is no harm in it. The fact that marriage is half of religion means that the married person has safeguarded his private parts, and thereby completed half of his religion. It does not mean that an unmarried person has incomplete faith.