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) divorced Hafsah (may Allah be pleased with her). When this reached Umar (may Allah be pleased with him), he put dust on his head and said: "O son of al-Khattab! After this, Allah will not care about you at all." Then Jibril (peace be upon him) descended upon the Prophet (peace and blessings be upon him) and said: Allah commands you to take Hafsah (may Allah be pleased with her) back, out of mercy for Umar (may Allah be pleased with him).
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19611