Among the necessary causes of happiness and the cessation of grief and worry is striving to remove the things that bring about grief and acquire those things that bring about happiness. This is achieved by forgetting the unpleasant things that have passed and he has no power to bring them back, and knowing that occupying his mind with them is meaningless, in fact it is stupidity bordering on lunacy. Therefore he has to struggle with his mind not to think of them. He should also struggle with his mind not to worry over the future, not to pay attention to illusions of poverty, fear or other unpleasant things he is imagining will descend on him in the future, whether good or evil, or pleasure or pain; this is in the Hands of Allah alone. The slave has no control over it. His only due is to struggle to accomplish what will benefit him in the future, and ward off harm from him. He should also know that when the slave turns his mind away from worrying over the future of his affairs, and relies on his Lord for its betterment, and is satisfied that his Lord will do that for him, his heart will be tranquil and his condition will be good, and his worries and anxieties will vanish.
Among the most beneficial things to do concerning the future of one’s affairs is to be saying the prayer that the Prophet, peace and blessings of Allah be upon him, who used to say,
“O Allah! Make my religion which is my strength and invincibility good for me, and make my world, wherein is my livelihood, good for me, and make my hereafter, which is my final abode, good for me. And make my living an increase for me in all that is good, and make my death a repose for me from every ill.” (Muslim)
And also his saying:
“O Allah! It is Your mercy that I have hope in, so do not leave me to myself even for the blink of an eye, and make good my affairs, all of them; there is no god worthy of being worshipped but You.” (Abu Dawud)
If the slave says this dua, which entails seeking the betterment of his future both in terms of his religion and his worldly affairs, if he says that with a mindful and aware heart, and a true and sincere intention, coupled with an earnest struggle to achieve it, Allah will definitely materialise for him and what he has asked for and hoped in and struggled to achieve. As a result, his worry will change to happiness and delight.
Useful Ways of Leading a Happy Life by Shaykh Abdur Rahman bin Nasr As S’adi Pages 23-25