" لا يحل سلف وبيع ولا شرطان في بيع، ولا ربح ما لم يضمن ولا بيع ما ليس عندك"
The Prophet (peace and blessings be upon him) said:
"It is not permissible to combine a loan and a sale, nor to set two conditions in one sale, nor to take profit on something that is not under your liability, nor to sell what you do not have."
Hadith Referenceصحیح الجامع الصغیر / حرف اللام ألف / 7644