Nothing exists except by the will and decree of Allaah
Question

What things affect Qadr (what has already been written for us)?.
Praise be to Allah.Nothing exists except by the will and decree of Allaah, because Allaah says (interpretation of the meaning):
“No calamity befalls on the earth or in yourselves but it is inscribed in the Book of Decrees (Al Lawh Al Mahfooz) before We bring it into existence. Verily, that is easy for Allaah”
[al-Hadeed 57:22]
And the Prophet (peace and blessings of Allaah be upon him) said: “The pens have been lifted and the pages have dried.” Narrated and classed as saheeh by al-Tirmidhi (2516), from the hadeeth of Ibn ‘Abbaas.
Al-Mubaarakfoori said:
“The pens have been lifted and the pages have dried” means, What has been decreed has been written in al-Lawh al-Mahfooz (the Book of Decrees), and nothing else will be written after that is finished.
Tuhfat al-Ahwadhi, 7/186
The writing is of two types: one kind which cannot be altered or changed, which is what is in al-Lawh al-Mahfooz, and a type which may be altered or changed, which is in the hands of the angels. And the ultimate outcome is what is written in al-Lawh al-Mahfooz. This is one of the meanings of the words of Allaah (interpretation of the meaning):
“Allaah blots out what He wills and confirms (what He wills). And with Him is the Mother of the Book (Al Lawh Al Mahfooz)”
[al-Ra’d 13:39]
Hence we can understand what was narrated in the Sunnah, that upholding family ties increases one’s lifespan or increases one’s provision; or that du’aa’ can alter the divine decree. For Allaah knows whether His slave will uphold the ties of kinship or make du’aa’, so He writes in al-Lawh al-Mahfooz that this person will have more provision or a longer life span.
Shaykh al-Islam Ibn Taymiyah was asked:
Can provision increase or decrease? Is provision what a person eats or possesses?
He replied:
Provision is of two types:
1 – That which Allaah knows He will provide, which cannot be changed.
2 – That which He has prescribed and told to the angels. This may increase or decrease depending on causes. If Allaah commands the angels to write provision for a person if he upholds the ties of kinship, Allaah will increase his provision because of that. It was proven in al-Saheeh that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever would like his provision to be increased and his life span to be extended, let him uphold the ties of kinship.” Similarly the life span of Dawood was extended by sixty years and Allaah made it one hundred years, after it was originally forty. This is as ‘Umar said: “O Allaah, if you have decreed that I am to be doomed, then erase that and make me one of those who are to be blessed, because You blot out whatever You will and confirm whatever You will.” Similarly Allaah said of Nooh (interpretation of the meaning):
“That you should worship Allaah (Alone), fear (be dutiful to) Him, and obey me,
He (Allaah) will forgive you of your sins and respite you to an appointed term”
[Nooh 71:3-4]
And there is a great deal of corroborating evidence. The means of acquiring provision comes under the heading of that which Allaah has decreed. If it has been decreed that a person will earn his provision by means of his work and efforts, then Allaah will cause him to work and strive, and that which is decreed for him by means of his work will not come to him without him working to earn it. And what has been decreed for him without his having to earn it, such as an inheritance, will come to him without him working for it.
Work or striving is of two types: striving in work for the sake of earning a living, such as industry, farming and business; and striving in du’a’, putting one's trust in Allaah, treating others kindly, and so on. Allaah will help His slave so long as His slave helps his brother.
Majmoo’ al-Fataawa, 8/540, 541 .