Sayyiduna Salamah bin Sakhr (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "If the one who made zihar has intercourse with his wife before paying the expiation, only one expiation is due from him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الظهار / 15258