‏الأيمان : Hadeeth No:4057 'Adi b. Hatim reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: He who took an oath, but he found something else better than that, should do that which is better and break his oath....

‏البيوع : Hadeeth No:3697 Ibn 'Umar (Allaah be pleased with them) reported Allaah's Messenger (sallAllaahu alayhi wa sallam) having forbidden Muzabana, and Muzabana implies the selling of dry dates for fresh dates on the tree with a definite measure (making it clear) that in case it increases, it belongs to me and if it is l...