Is it obligatory to perform the prostration of recitation (Sujud al-Tilawah) upon hearing it from a cassette tape of the Noble Qur'an, and what if the listener is not in a state of ritual purity (wudu')?

The conditions for the prostration of recitation (Sajdat al-Tilawah) are the same as those for a supererogatory prayer, namely: purification from both major and minor ritual impurity, covering the 'awrah (private parts), facing the qiblah, and having the intention. This is the madhhab (school of thought) of the four Imams, and no disagreement is known concerning it, except for what was narrated from Uthman ibn Affan (may Allah be pleased with him), Sa'id ibn al-Musayyab, and Al-Sha'bi. However, ablution is not obligatory if one hears the prostration verse while not in a state of purity. It is required that the hearing be direct; therefore, prostration is not valid if heard from a television, radio, or recording.