فنازعت أقدار الحق بالحق للحق، والرجل من يكون منازعاً للقدر، لا من يكون موافقاً للقدر‏

“I have fought against what was destined by al-Haqq, with al-Haqq, for al-Haqq. Men are those who battle against fate, not those who go along with it.” - Abd al-Qadir al-Jilani (r.a.)

Ibn Taymiyya said,

“What the Shaykh - may Allah’s mercy be upon him- said, is what Allah and His Messenger commanded, but many men have erred, for they might see what was destined for someone from sins and wrong acts, even of disbelief, and see that this goes according to the will of Allah, and that what He ordains and destines comes from the fact of His Lordship and the fact that what He wills must happen. So they think that surrendering to that, going along with it, and accepting it, is a way (deen), a path (tariq), and an act of worship (ibada). In this they become like the mushrikeen who said, “Had Allah willed, we had not ascribed (unto Him) partners neither had our fathers, nor had we forbidden aught (of what He made lawful)” and they said “Shall we then feed those whom, if Allah had so willed, He would have fed, (Himself)?” and they said, “Had Al-Rahman so wanted, we would not have worshiped them.“

Had they been guided, they would have known that we were commanded to accept destiny and have patience when a calamity happens, like poverty, illness, or fear. He Most High said, “No calamity befalleth save by Allah’s leave. And whosoever believeth in Allah, He guideth his heart.” As one of our pious predecessors said, “He is the man who is afflicted with an affliction and knows that it is from Allah so he accepts it and resigns to it.” And He Most High said, “Naught of disaster befalleth in the earth or in yourselves but it is in a Book before we bring it into being - Lo! that is easy for Allah - That ye grieve not for the sake of that which hath escaped you, nor yet exult because of that which hath been given.“

As for sins, a servant may not sin, and if he sinned, he must ask Allah’s forgiveness and repent, for one must repent from fault and have patience with calamities…. And so it is with the sins of (other people). The servant must command that which is good and forbid that which is evil- according to his ability- and to struggle against the kuffar and hypocrites in the cause of Allah, to support the awliya of Allah and to take as enemies the enemies of Allah, to love in Allah and hate in Allah…

…They must struggle in order to uphold His Deen, asking His help in that, removing with that that which was destined of bad things… just as man removes the present hunger with food, and keeps away with it future hunger, and likewise, if the time of cold weather comes, he keeps the cold away through clothing, and likewise all that man wants is used to keep away something that man does not want. As they said to the Prophet (pbuh), “Oh Messenger of Allah, you see the medicines that we take, the recitations that we use for healing, and precautions with which we protect ourselves, do they keep away anything that Allah has destined?” So he said, “they are part of what Allah has destined.” And among the hadith: “Supplication and affliction will meet and fight between the Sky and the Earth.” This is the state of those who believe in Allah and His Messenger, and all that is part of worship.

[Summarized, and translated, from Ibn Taymiyyah’s Fatawa, vol 10: www.al-eman.com/islamlib/viewchp.asp?BID=252&CID=191#s1]