The ruling on performing tawaf with najasah (physical impurity) on clothing or the body is a matter of scholarly discussion that relates to the broader question of how closely tawaf mirrors the requirements of salah (shalat). The majority of scholars hold that while purity from hadath (ritual impurity requiring wudhu) is required or strongly sunnah for tawaf, purity from najasah (physical impurities like blood, urine, etc.) follows similar principles as for shalat — it is required when one is aware of it and able to remove it.
Sheikh Ibn Uthaymeen explained that if a jamaah haji discovers najasah on their clothing during tawaf, they should remove it if possible — for example, by removing the affected garment or washing the spot — and continue their tawaf without restarting. If they cannot remove it, they should complete their tawaf, and it is valid based on the principle of necessity and hardship. If they only discover the najasah after completing tawaf, the tawaf is valid without question, as one is not accountable for what they did not know.
The Permanent Committee ruled that purity from both hadath and najasah is required for tawaf in principle, but they distinguished between knowing and unknowing states. A jamaah haji who unknowingly carries najasah has a valid tawaf. This is analogous to the ruling on shalat — if a person prays with najasah without knowing, their shalat is valid according to the stronger opinion. Given the extreme crowding during Haji, maintaining complete purity from najasah is exceptionally difficult, and scholars recognize this practical reality.