Benevolence (Ihsan) has been emphasized over and over again in Islamic teachings. The Qur'an says:
Indeed Allah ordains justice and benevolence. (16:90)
Benevolent behaviour is considered a natural response of a believer to the spiritual realization of the tremendous blessings he received from his Creator and Nourisher without being entitled to them. In other words, a true believer is prepared to give to others, over and above what he owes to them on the principle of justice to express his gratitude to God Almighty for having done the same to him on a much larger scale. The Qur'an, when urging the believer to spend in the way of Allah, says:
And spend [to earn the pleasure of Allah] out of the means of sustenance that We have provided you with. (63:10)*
It must, however, be clarified that benevolence is a bonus-value which in order to be valid must always succeed justice. Otherwise 'benevolence is likely to undermine benevolence'. In other words benevolence starts from the basis that justice has already been done. If an employer, for instance, treats his own employees badly and keeps them underpaid (ie contravenes the spirit of justice), no matter how much he may spend in avenues of charity, his behaviour would be unacceptable to Islam.
It is not always easy to draw a clear line of demarcation between justice and benevolence. When an attitude of benevolence is urgently needed to alleviate the hardship of the needy, the act of benevolence should more properly be considered binding and, therefore, counted as a requirement of justice. Parting with 2.5% every year from the savings of legitimately earned wealth to cater for the needs of other (Zakah) may appear an act of benevolence from the point of view of the giver, but it is no more than simple justice (requirement of justice) if one considers the need and deprivation of the fellow human beings. Likewise, parting with one's savings to help meet a need of another person through an interest-free loan, although apparently an act of benevolence, is involuntary as far as restriction on demanding interest is concerned. Thus, such apparently voluntary virtue, if neglected, would violate the peculiar requirements of Islamic justice have been made involuntary for the believer in Islam (check). This clear demarcation of justice and benevolence precludes the possibility of the two ever overlapping practically since the role of the latter emerges only when the domain of the former ends. In the apparently 'grey areas', the intensity and urgency of the needy and the possibility of the potential helper's ability to come to his aid and his own circumstances would ultimately decide whether an action or lack of it was relating to justice or to benevolence.
* These or similar words have been repeated at least eight times in the Qur'an. See 2:254, 4:39, 13:22, 35:29, 65:7, 36:47 & 57:7.