Is it permissible to recite the Qur’an without observing the madd (prolongations), while adhering to other rules of Tajweed? And is omitting the madd considered a sin?

It is recommended for the reciter of the Quran to chant (tartīl) and ponder, and it is permissible for him to recite quickly (hadr) while observing the rules of tajweed.

As for the Madd (prolongations): Al-Madd Al-Munfaṣil (disconnected prolongation): It is permissible to shorten it. Al-Madd Al-Muttaṣil (connected prolongation): The reciters have agreed on prolonging it, but differed on its measure. It is not permissible to shorten it. It has been authentically reported from the Prophet (peace and blessings be upon him) that he commanded its prolongation.