Praise be to Allaah.
If you know that one of the couple does not pray, then do not perform the marriage contract, because not praying is kufr. The Prophet (peace and blessings of Allaah be upon him) said, “Between a man and shirk and kufr there stands his giving up prayer” (narrated by al-Bukhaari and Muslim in their Saheehs). And the Prophet (peace and blessings of Allaah be upon him) said: “The covenant that stands between us and them is salaah; whoever neglects it is guilty of kufr” (narrated by Imaam Ahmad and the fours authors of Sunan, with a saheeh isnaad). We ask Allaah to put the affairs of the Muslims right, and to guide those who have gone astray, for He is All-Hearing and Ever Near.