Alqamah bin Qays narrates that Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "Whoever wishes, I am ready to contend with him firmly over this: that the verse 'And for those who are pregnant, their term is until they deliver their burden' [Surah al-Talaq: 4] was revealed after this verse about the widow: 'And those of you who die and leave behind wives, they shall wait by themselves for four months and ten days' [Surah al-Baqarah: 234]."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9607