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Allah says in the Quran...
Who is it that will lend to Allah a goodly loan, so that He may give it increase manifold? (Do not fear poverty) Allah straitens and enlarges (your provision), and to Him you will return. (al-baqarah: 245)
explanation of the verse...
The act of spending for the cause of Allah has been interpreted as advancing loan to Allah Ta’ala, which means that, just as the return of a loan is obligatory, the recompense and reward for spending in charity is a certainty.
That is why Sadaqah has been termed as loan. Umar Radhiallaho anho has stated that giving a loan to Allah Ta’ala means spending in charity. Ibne Mas’ood Radhiallaho anho has said that, when the above Ayat was revealed, Abu Dahda Ansaari Radhiallaho anho came to Rasulullah Sallallaho alaihe wasallam and submitted, "O Rasulullah, does Allah Jalla Shanohu desire a loan from us?" Rasulullah Sallallaho alaihe wasallam replied, "Certainly so" He then said, "Please give me your hand" (for making a promise).
Rasulullah Sallallaho alaihe wasallam stretched out his hand towards him and Abu Dahdah Radhiallaho anho, taking it in his own hand as a gesture of a vow, said that he was giving his garden to Allah Ta’ala as a loan. That garden had six hundred date-palms and his wife and children were living in it.
Abu Dahdah Radhiallaho anho went to the garden, called his wife Umme Dahdah Radiyallaho anha and told her that they had to leave the garden as it had been given away to their ‘Lord’ (Allah Ta’ala). Another Hadith by Abu Hurairah Radhiallaho anho says that Rasulullah Sallallaho alaihe wasallam distributed that garden among some orphans.
Still another Hadith says that when the sacred Ayat was revealed, saying: "Whoever earned a single virtue would receive ten times the reward for it", Rasulullah Sallallaho alaihe wasallam made a dua, "O Allah! Compensate my ‘Ummah’ even more than that". As a result this Ayat was revealed. Rasulullah Sallallaho alaihe wasallam again implored Allah for a further increase.
Thereupon the Ayat which has been explained at serial No. 7 below, was revealed. Rasulullah Sallallaho alaihe wasallam again made supplication saying, "O Allah, increase the reward of my Ummah" Thereupon the Ayat was revealed "That whoever is steadfast will receive a full return, which will be boundless." (az-Zumar: 19)
Another Hadith says that an angel calls out, "Whoever offers a loan today will receive a full compensation tomorrow" Another Hadith says that Allah Jallah Shanohu proclaims, "O man, entrust your treasures to me for safe custody; none of these will catch fire, nor sink, nor be stolen, you will receive these back from Me at the time when your need for them will be the greatest". (Durre manthur
http://www.radioislam.org.za/a/index.php/library/172-zakaah/11761-sadaqah-virtues-of-spending.html
excerpts taken from FAZAIL E SADAQAT..
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