It is narrated from Amr bin Dinar (may Allah have mercy on him) that Ibn al-Zubayr (may Allah be pleased with them both) used to give her (the pregnant widow) maintenance, until it reached him that Abdullah bin Abbas (may Allah be pleased with them both) said that she has no maintenance. So he retracted that statement of his, meaning that the pregnant woman whose husband dies is entitled to maintenance. Ata' bin Abi Rabah (may Allah have mercy on him) narrated it from Abdullah bin Abbas (may Allah be pleased with them both), who said that she has no maintenance; the inheritance has become due.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15478