that the Messenger of Allah said: "It is not permissible to lend on the condition of a sale, or to have two conditions in one transaction, or to sell what you do not have." (Sahih
"I asked the Prophet "O Messenger of Allah, a man may come to me and ask me to sell him something that I do not have. Can I sell it to him then go and buy it from the market?' He said: 'Do not sell what you do not have.'''
'We used to pay in advance during the time of the Messenger of Allah and Abu Bakr and 'Umar, for wheat, barley and dates, paying people whom we did not know if they had those things or not.'''Ibn Abza said meaning, similarly.
"Abu Burdah and 'Abdullah bin Shaddad argued about payment in advance. They sent me to Ibn Abi Awfa and I asked him (about that). He said: 'We used to pay in advance during the time of the Messenger of Allah and Abu Bakr and 'Umar, for wheat, barley, raisins and dates, paying people whom we did not see it with them." And I asked Ibn Abza and he said something similar to that.
"I heard Ibn 'Abbas say: 'When the Prophet came (to al-Madinah), they used to pay in advance for dates, two or three years in advance. He forbade them that and said: 'whoever pays in advance for dates, let him pay for a known amount or a known weight, to be delivered at a known time'''
"Go and buy a young camel for him." He came and said: "I could only get a Raba camel of good quality." He said: "Give it to him, for the best of the Muslims is the one who is best in repaying."
أَخْبَرَنَا عَمْرُو بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ سَلَمَةَ بْنِ كُهَيْلٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ كَانَ لِرَجُلٍ عَلَى النَّبِيِّ صلى الله عليه وسلم سِنٌّ مِنَ الإِبِلِ فَجَاءَ يَتَقَاضَاهُ فَقَالَ " أَعْطُوهُ " . فَلَمْ يَجِدُوا إِلاَّ سِنًّا فَوْقَ سِنِّهِ قَالَ " أَعْطُوهُ " . فَقَالَ أَوْفَيْتَنِي . فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّ خِيَارَكُمْ أَحْسَنُكُمْ قَضَاءً " .
"A man had lent a camel of a certain age to the Prophet and he came to get it back. He said: "Give it to him" But they could only find a camel that was older than it. He said: "Give it to him." He said: "You have repaid me well," The Messenger of Allah said; "The best of you is the one who is best in repaying"