It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyidah Duba'ah bint al-Zubayr bin Abd al-Muttalib (may Allah be pleased with her) came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah! I intend to perform Hajj; may I make a condition? He (peace and blessings be upon him) said: "Yes." She asked: How should I say it? He (peace and blessings be upon him) said: "Say: 'Labbayka Allahumma labbayk' (Here I am, O Allah, here I am); my place of leaving ihram is wherever You hold me back."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11859