Hadith 10:278
Abu Bakr narrated to us, he said: Ghundar narrated to us, from Shu'bah, from 'Abd al-Khaliq, from Hammad, he said: If a man writes to his wife, "When this letter of mine reaches you, then you are divorced," and the letter does not reach her, then she is not divorced. If he writes, "Amma ba'd (as for what follows), you are divorced," Ibn Shubruma said: She is divorced.
حدثنا أبو بكر قال نا غندر عن شعبة عن عبد الخالق عن حماد قال إذا كتب الرجل إلى امرأته إذا أتاك كتابي هذا فأنت طالق فإن لم يأتها الكتاب فليس بطالق فإن كتب أما بعد فانت طالق قال بن شبرمة فهي طالق