Sayyidah Aishah (may Allah be pleased with her) said: When the Messenger of Allah (peace and blessings be upon him) intended to travel, he would cast lots among his wives, and whoever's lot came out, he would take her with him. And he (peace and blessings be upon him) allotted turns to all his wives except Sayyidah Sawdah bint Zam'ah (may Allah be pleased with her), because Sawdah bint Zam'ah (may Allah be pleased with her) had gifted her turn to Sayyidah Aishah (may Allah be pleased with her), seeking the pleasure of the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14733