It is narrated from Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) once divorced Sayyidah Hafsah (may Allah be pleased with her). When this news reached Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), he put dust on his head and said: O Ibn al-Khattab, after this Allah will give you no importance. Thereupon Jibril (peace be upon him) descended and said: Allah Almighty commands you to take Sayyidah Hafsah back in marriage, out of mercy for Umar.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14876