Hadith.4022 - Muhammad ibn Qays narrated from Abu Ja'far Imam Muhammad ibn Ali Al-Baqir (as) that Commander of the Faithful (as) said
"Whoever sells a commodity and says, 'Its price is such and such if paid immediately, and its price is such and such if paid later,' then take it at whichever price you wish and make it a single transaction."
Then Imam (as) said: "He is only entitled to the lower price, even if it is on credit."