Musnad Ahmad 27:1050

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from 'Abdullah ibn Dinar, who said: I heard Ibn 'Umar saying: "The Messenger of Allah, may Allah bless him and grant him peace, forbade the selling of fruit or palm trees until their soundness becomes apparent." It was said to Ibn 'Umar: "What is their soundness?" He said: "Their blight departs."