It is narrated from al-Sha'bi (may Allah have mercy on him) that Ali (may Allah be pleased with him) would move a woman whose husband had died, without waiting (for her 'iddah to end). And it is narrated from Ibn Mahdi, from Sufyan, from Firas, from al-Sha'bi: al-Sha'bi (may Allah have mercy on him) said: Ali (may Allah be pleased with him) moved Umm Kulthum (may Allah be pleased with her) seven nights after Umar (may Allah be pleased with him) was killed. Sufyan al-Thawri (may Allah have mercy on him) narrated it in his Jami' and said: That was because she was in the governor's residence.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15508