Don't Be Sad Over What Missed You
And beware of feeling regret over past affairs which were not decreed for you, or loss of health, wealth, a job and the likes. Let your focus and concern be rectifying the actions of the day you are in; for indeed a person is the offspring of their day - they do not grieve over the past, nor do they look distantly in to the future where it is of no benefit to them.
And be truthful, fulfill your oaths and promises and be just in all of your dealings. Give people their rights in full and in abundance. Do so, with a soul at peace and an īmān (faith) that is truthful and sincere.
And busy yourself with your own shortcomings and your own affairs above the shortcomings and affairs of others.
And deal with every individual person according to what is appropriate for their mental state; whether young or old, male or female, the ruling class or the ruled.
Be gentle and merciful with every individual - even the wild or domesticated animals. Verily Allāh is Merciful only to His Slaves who show mercy.
Strive constantly in all your endeavors and affairs. Keep your mind open to any and every benefit - whether religious or worldly. (end quote)
Reference: Majmū' Mu'allafātihi [21/258]
Translated by our Brother Abul Layth Ziyaad Qureshi