Imam al-Shafi'i (may Allah have mercy on him) said: "Allah, the Blessed and Exalted, says: 'When you divorce women, divorce them at (the start of) their waiting period.' [Surah al-Talaq: 1]
It has also been read 'li-qubuli 'iddatihinna' (at the approach of their waiting period), and these two (readings) do not differ from each other in meaning."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / Q14902