Al-Baqarah (The Cow) - Chapter 2: Verse 261
"The likeness of the wealth of those who spend it in the way of Allah is as the likeness of a grain of corn that grows seven ears, each ear having a hundred grains. Allah gives manifold increase to whom He wills; and Allah is all-Embracing, all-Knowing."
Fi sabilillah (in the cause of Allah) in Quranic terminology covers all works undertaken for the benefit of Islam and Muslims. Depending on the conditions, a work may be high or low on the list of priorities, but whatever is done abiding by the Islamic Shariah and seeking the pleasure of Allah, is covered by the term fi sabilillah — in the cause of Allah.
Like a grain of corn having seven ears and each ear a hundred grains, every good deed will be similarly rewarded seven hundred times over in the Hereafter. This has also been elucidated in various sayings of the Prophet, peace be upon him, where he is reported to have said that every good deed will be rewarded from ten to seven hundred times. This difference in reward is obviously based on the nature of every deed, the prevalent conditions of life, and the apparent as well as the inner condition of the doer of the deed. An act of virtue done under difficult conditions and scarcity of resources will naturally attract a higher reward than the one done under relatively easy conditions, prosperity and affluence. The feelings of the doers will also have an impact on their reward. There will be a difference in the reward for a good deed done willingly and cheerfully and the one that is rather done reluctantly and half-heartedly. The verse refers to the highest reward while saying, "Allah gives manifold increase to whom He pleases." Whatever Allah wishes or desires, it is never in contravention to demands of His justice and wisdom. In other words, He wishes this manifold increase only for those of His servants who deserve and truly qualify for it under the law prescribed by Him in this regard.
Considering their own limitations, humans may be surprised at the generosity of the reward they receive, but Allah is infinitely great, all-encompassing. The verse also reminds us that whatever good deed, small or great, secret or public one does, Allah is fully aware of it. Every worker should therefore rest assured that he will be fully rewarded for all his good works. Not only are the treasures of the Giver infinite and inexhaustible, His knowledge also comprehends all. There is no cause therefore for anyone to be worried about losing their due reward; everyone shall be rewarded in full.
"Pondering Over The Qur'an: Surah al-Fatiha and Surah al-Baqarah" - Amin Ahsan Islahi