It is narrated from Hazrat Ata (may Allah have mercy on him) that if someone says to another: "You have unlawful relations with your wife," then there is no hadd (prescribed punishment) for this.
Hadith Referenceسنن سعید بن منصور / كتاب النكاح / 1811
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 634، وابن أبى شيبة فى «مصنفه» برقم: 29252»