Sayyidah Umm Salamah (may Allah be pleased with her) said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Whoever says the talbiyah for Hajj or Umrah from al-Masjid al-Aqsa to al-Masjid al-Haram, his past and future sins will be forgiven, or Paradise becomes obligatory for him." (The narrator Abdullah was unsure which of the two he said.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8926