It is narrated from Ibn Umar (may Allah be pleased with them both) that a divorced woman and a woman whose husband has died should count the waiting period from the very day on which her husband died or on which she was divorced.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15445
It is narrated from Abdullah bin Mas'ud (may Allah be pleased with him) that the waiting period of a divorced woman is from the time she is divorced, and the waiting period of a woman whose husband has died is from the time her husband died.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15446
It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that she should count from the day she was divorced or the day her husband died.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15447
It is narrated from Sa'id bin Jubayr, Sa'id bin al-Musayyab and Sulayman bin Yasar (may Allah have mercy on them) that she should count the waiting period from the very day on which she was divorced or on which her husband died.
Imam al-Bayhaqi (may Allah have mercy on him) said: This is the view of Ata bin Abi Rabah, Ibrahim al-Nakha'i, al-Zuhri and others.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15448
It is narrated from Abu Sadiq that Ali (may Allah be pleased with him) said: "She should count from the day the news reaches her." This is the well-known narration from Ali (may Allah be pleased with him), and Imam al-Sha'bi (may Allah have mercy on him) also reported it likewise from Ali (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15449