Key حج dhikr includes the تلبیہ (from احرام to stoning), the عرفات declaration of tawheed, takbirat al-Tashreeq on the 11th-13th, and personal دعا during طواف.
Dhikr (remembrance of Allah) is the spiritual essence of حج, transforming physical actions into acts of deep worship. The most important dhikr during حج is the تلبیہ: 'Labbayk Allahumma labbayk, labbayk la sharika laka labbayk, innal hamda wan-ni'mata laka wal-mulk, la sharika lak.' This should be recited frequently and aloud (for men) from the moment of entering احرام until the stoning of جمرات al-Aqaba on the 10th.
At عرفات, نبی کریم (صلی اللہ علیہ وسلم) said: 'The best دعا is on the Day of عرفات, and the best thing that I and the prophets before me said is: La ilaha illa Allahu wahdahu la sharika lah, lahul mulku wa lahul hamdu wa huwa ala kulli shay'in qadir.' During the days of Tashreeq (11th-13th), the takbirat of Tashreeq are prescribed: 'Allahu Akbar, Allahu Akbar, la ilaha illa Allah, Allahu Akbar, Allahu Akbar, wa lillahil hamd.' During طواف, there is no specific prescribed dhikr — scholars advise making personal دعا, reciting قرآن, or any dhikr that moves your heart. Between the Yemeni corner and the حجر اسود, the sunnah دعا is: 'Rabbana atina fid-dunya hasanah wa fil-akhirati hasanah waqina adhab al-nar.'
Source: Sunan al-Tirmidhi; Muwatta of Imam Malik; Sahih Muslim