Husayn bin Qabisah narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that he said: "The impotent man (one unable to have intercourse) is to be given a respite of one year; if he consummates (the marriage) with her, well and good; otherwise they are to be separated."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9669