Is it obligatory for the pilgrim to sacrifice an animal?

Slaughter is not obligatory for every pilgrim, but rather for the Qarin (pilgrim performing Hajj and Umrah concurrently) and the Mutamatti' (pilgrim performing Umrah then Hajj). It may become obligatory for a pilgrim due to a contingent reason, such as neglecting an obligatory rite of the pilgrimage or committing a prohibited act that necessitates slaughter.