Hasan (may Allah have mercy on him) said: "If the one who has pronounced zihar has intercourse with his wife before offering the expiation, it is obligatory for him to stop, seek forgiveness from Allah, and offer one expiation."
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 3005
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 1828، وعبد الرزاق فى «مصنفه» برقم: 11523، 11524»