Is it obligatory to sit for a few moments when called from behind or when leaving a place to avoid bad luck?

What you heard about ṭīrah (superstitious belief in omens) is incorrect; rather, it is from the practices of Jāhiliyyah (pre-Islamic ignorance) and polytheism, which the Prophet, peace and blessings be upon him, forbade, because it contradicts the perfection of Tawḥīd (monotheism). Ṭīrah is polytheism, and it is obligatory to rely on Allah to repel it. The prophetic traditions have warned against ṭīrah and described it as polytheism, and they have clarified that the best of it is fa’l (good omen), which is a good word. If a Muslim sees something he dislikes, he should say: “O Allah, none brings good deeds except You, and none repels evil deeds except You, and there is no might or power except with You.” And whoever is turned back from his need by ṭīrah has committed polytheism, and its expiation is for him to say: “O Allah, there is no good except Your good, and no ṭayr (omen) except Your ṭayr, and there is no god other than You.” Whoever abandons ṭīrah and proceeds with his affair will not be harmed by it, but whoever surrenders to its whispers may be punished.