Ma'arif al-Qur'an
Mufti Muhammad Shafi(5) Verse 271: إِن تُبْدُوا الصَّدَقَاتِ فَنِعِمَّا هِيَ (الی قولہ) وَاللَّـهُ بِمَا تَعْمَلُونَ خَبِير : "If you give the alms openly, it is good enough, ... and Allah is All-Aware of what you do"Obviously, this verse covers all types of charity, whether obligatory or supererogatory, and it is more preferable to perform all of them as secretly as possible. To observe secrecy in a charitable act has religious merits, because it is far from the possibility of riya' ریاء (show off), and more graceful for the receiver who can feel shy about receiving charity in public. It is also beneficial from an earthly point of view, because it does not disclose the amount of wealth one owns.
It should, however, be kept in mind that the preferability of observing secrecy is a matter of principle. There may be situations where it becomes more preferable to perform an act of charity openly for some external reasons, such as removing some accusation (of not paying زکاۃ Zakah, for instance) or to persuade others to follow the example. Such exceptional cases do not negate the basic principle in any way.
Immediately after the instruction of concealing the 'Sadaqat صداقات ', the holy verse says, وَيُكَفِّرُ عَنكُم مِّن سَيِّئَاتِكُمْ (This will write off part of your sins). It does not mean that the expiation of evil-deeds is confined to the charity made in secret only. In fact, a charity made in public also carries the same benefit. But the reference to expiation here is in the context that even if someone feels a secret charity as useless in this world, he should not feel depressed, because Allah will forgive his sins, and that is a great gain for him.