What is the ruling concerning my work if it involves a mixture of lawful and unlawful elements, and can one benefit from mixed wealth, and what is the preponderant opinion among the sayings of the scholars on this matter?

Money acquired through unlawful means is not permissible for its owner unless he is poor and in need. In such a case, he is allowed to spend it on himself to the extent of his need. This is the fatwa given by Shaykh al-Islam Ibn Taymiyyah, while the opinion that it is permissible to benefit from unlawful money absolutely is wrongly attributed to him. The responsibility of the common person is absolved if he acts upon the fatwa of a trustworthy scholar, even if the scholar erred in his ijtihad (independent reasoning), as long as the common person is not aware of this error.