Musannaf Ibn Abi Shaybah

Hazrat Ibn Abbas (may Allah be pleased with them both), in the explanation of the verse of the Holy Qur'an { فَطَلِّقُوہُنَّ لِعِدَّتِہِنَّ }, says that a woman should be divorced at the beginning of her waiting period (so that it is easy for her to count the waiting period).