Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) used to recite these words: "Divorce them" 'qubula 'iddatihinna' or 'li-qubuli 'iddatihinna' (at the start of their waiting period) [Surah al-Talaq: 1].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14904