ASSALAM ALAIKUM..
The book of destiny:- Sahih muslim, Bukhari.
Abdullah (b. Mas'ud) reported that Allah's Messenger (may peace be upon him) who is the most truthful (of the human beings) and his being truthful (is a fact) said: Verily your creation is on this wise. The constituents of one of you are collected for forty days in his mother's womb in the form of blood, after which it becomes a clot of blood in another period of forty days. Then it becomes a lump of flesh and forty days later Allah sends His angel to it with instructions concerning four things, so the angel writes down his livelihood, his death, his deeds, his fortune and misfortune. By Him, besides Whom there is no god, that one amongst you acts like the people deserving Paradise until between him and Paradise there remains but the distance of a cubit, when suddenly the writing of destiny overcomes him and he begins to act like the denizens of Hell and thus enters Hell, and another one acts in the way of the denizens of Hell, until there remains between him and Hell a distance of a cubit that the writing of destiny overcomes him and then he begins to act like the people of Paradise and enters Paradise.
According this hadith, these r the things wch r fixed by ALLAH.
The book of destiny:- sahih muslim, bukhari.
Abu Tufail reported: I visited Abu Sariha Hudhaifa b. Usaid al-Ghifari who said: I listened with these two ears of mine Allahs Messenger (may peace be upon him) as saying: The semen stays in the womb for forty nights, then the angel, gives it a shape. Zubair said: I think that he said: One who fashions that and decides whether he would be male or female. Then he (the angel) says: Would his limbs be full or imperfect? And then the Lord makes thein full and perfect or otherwise as He desires. Then he says: My Lord, what about his livelihood, and his death and what about his disposition? And then the Lord decides about his misfortune and fortune
The book of destiny:- Sahih muslim, Bukhari
Hudhaifa b. Usaid reported directly from Allah's Messenger (may peace be upon him) that lie said: When the drop of (semen) remains in the womb for forty or fifty (days) or forty nights, the angel comes and says: My Lord, will he be good or evil? And both these things would be written. Then the angel says: My Lord, would he be male or female? And both these things are written. And his deeds and actions, his death, his livelihood; these are also recorded. Then his document of destiny is rolled and there is no, addition to and subtraction from it.
The book of destiny:- Sahih muslim, bukhari.
Ali reported: We were in a funeral in the graveyard of Gharqad that Allah's Messenger (may peace be upon him) came to us and we sat around him. He had a stick with him. He lowered his head and began to scratch the earth with his stick, and then raid: There is not one amongst you whom a scat in Paradise or Hell has not been allotted and about whom it has not been written down whether he would be an evil person or a blessed person. A person said: Allah's Messenger, should we not then depend upon our destiny and abandon our deeds? Thereupon he said: Acts of everyone will be facilitated in, that which has been created for him so that whoever belongs to the company of the blessed will have good works made easier for himand whoever belongs to the unfortunate ones will have evil acts made easier for him. He then recited this verse (from the Qur'an):" Then, who gives to the needy and guards against evil and accepts the excellent (the truth of Islam and the path of righteousness it prescribes), We shall make easy for him the easy end and who is miserly and considers himself above need, We shall make easy for him the dificult end".
I hope the above hadiths are enough for us to understand about destiny and the things which we cant change. As in the last hadith our prophet mentioned the Quranic verse, from that we understand that its ALLAH one and only who can guide us to the straight path and protect us from fire. So u should always seek guidance and protection from hell fire from ALLAH..
ALLAH KNOWS BEST.