Marriage.
And among His signs is this, that He created for you mates from among yourselves that you may dwell in tranquility with them; and He has put love and mercy between your (hearts); verily in that are signs for those who reflect. [Qur'an 30:21]
The Holy Prophet Muhammad (peace and blessings be upon him) said:
"When a man marries, he has fulfilled half of his religion, so let him fear Allah regarding the remaining half."
( Marriage quotation from Bayhqi)