Hadith 1164B1

قَالَ مَالِكٌ فِي الْمُخَيَّرَةِ : إِذَا خَيَّرَهَا زَوْجُهَا، فَاخْتَارَتْ نَفْسَهَا، فَقَدْ طَلُقَتْ ثَلَاثًا، وَإِنْ قَالَ زَوْجُهَا : لَمْ أُخَيِّرْكِ إِلَّا وَاحِدَةً، فَلَيْسَ ذَلِكَ لَهُ، وَذَلِكَ أَحْسَنُ مَا سَمِعْتُ .
Imam Malik, may Allah have mercy on him, said regarding the woman who is given the choice (to separate): When her husband gives her the choice (to separate), and then she chooses herself (and leaves her husband), then she will have three divorces. If her husband says, "I only gave you the choice of one divorce and nothing more," then this statement will not be accepted in favor of the husband, and this is the best statement that I have heard.
Hadith Reference موطا امام مالك رواية يحييٰ / كتاب الطلاق / 1164B1
Hadith Takhrij «فواد عبدالباقي نمبر: 29 - كِتَابُ الطَّلَاقِ-ح: 30»