The Gemara in Masechet Eruvin (64) advises that one who comes upon a windfall profit, which might make him susceptible to the "evil eye" of jealousy and envy on the part of others, should protect his new wealth by allocating some of it for the purchase of a Sefer Torah. By spending some of the money on a long-term Mitzva, one gains protection from the harmful effects of the Ayin Ha'ra ("evil eye"). As the Gemara in Ketubot comments, "Melach Mammon Chaser" – the "salt," or means of preservation, of wealth is squandering it, meaning, allocating some of the money on worthy Mitzva causes.
The Gemara mentions several examples of a sudden windfall that requires protection from the "evil eye." One example is the case of the estate of a convert. According to Halacha, a convert to Judaism has no relatives and hence no inheritors; therefore, the first to seize his property after his death may keep those possessions. A person who acquires wealth by seizing the estate of a deceased convert must protect it from the effects of the Ayin Ha'ra. Other cases mentioned by the Gemara are a person whose one's wife suddenly falls into an inheritance, and a successful business deal which yields a large, quick profit. Additionally, the Gemara speaks of one who finds an expensive lost object, such as a large sum of money or valuable jewel. In all these situations, one is advised to protect himself from the Ayin Ha'ra by spending some of the money earned on a Mitzva.
The Ben Ish Chai (Rabbi Yosef Chaim of Baghdad, 1835-1909) raises a question concerning the Gemara's final example, of one who discovers a lost item. In all the other cases listed, the sudden profit is public knowledge; word spreads when a person passes on and leaves an inheritance, or when a major business deal is closed. But when a person walks in the street, discovers a diamond and puts it in his pocket, this windfall is not exposed to public view. Why, then, must the individual be concerned about Ayin Ha'ra in such a case? The Ben Ish Chai beautifully answers that in such a case, a person must guard himself against his own Ayin Ha'ra. Even if the profit does not become public knowledge, the individual's own "evil eye" towards the newly gained wealth renders it susceptible to the dangers of Ayin Ha'ra.
The Zohar (the principal text of Kabalah) writes in Parashat Naso, "Everything depends on Mazal [good fortune], including the Sefer Torah in the ark." This is generally understood to mean that Mazal governs even issues such as which Torah scroll will be removed from the ark on a given day for the Torah reading. However, the Maharam Shif (famous Talmudic commentator, 1605-1641) offers a different reading of this comment, in light of the Gemara's discussion in Masechet Erubin. He explains this comment to mean that even a Sefer Torah must be involved in a person's Mazal, when one enjoys good fortune. When a person suddenly comes upon wealth, he should allocate a portion towards the purchase of a Sefer Torah and thereby gain protection from the Ayin Ha'ra.
