It is narrated from Imam Sha'bi that Sayyiduna Umar (may Allah be pleased with him) said: O people! We do not know, it may be that we command you regarding matters which are not permissible for you, and it may be that we declare things forbidden for you which are actually lawful for you. The last verse revealed in the Noble Qur'an was about usury, and the Messenger of Allah (peace and blessings be upon him) did not explain it to us in detail before he passed away. Therefore, leave that which you are doubtful about, and adopt that which you have no doubt about (act upon it).