Muhammad bin Umar bin Abi Salamah (may Allah have mercy on him) said: Umm Salamah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), used to order us to make a stipulation when we performed Hajj.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10122