وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ لاَ يُخْرِجُ فِي زَكَاةِ الْفِطْرِ إِلاَّ التَّمْرَ إِلاَّ مَرَّةً وَاحِدَةً فَإِنَّهُ أَخْرَجَ شَعِيرًا ‏.‏

Yahya related to me from Malik from Nafi that Abdullah ibn Umar would always pay the zakat al-fitr in dates, except once, when he paid it in barley. Translation Not Available

Book Ref: Muwatta Imam Malik Book 17 Hadith 631
Web Ref:  Muwatta Imam Malik Book 17 Hadith 55