Narrated Sa'id bin al-Musaiyab regarding a man who finds nothing to spend on his wife:

"They are to be separated." Reported by Sa'id bin Mansur, from Sufyan, from Abu az-Zinad, from Sa'id bin al-Musaiyab. He said, "I asked Sa'id (bin al-Musaiyab), 'Is this Sunnah?' And he replied, 'Yes, it is Sunnah!'" [This Hadith is a strong Mursal (missing link after the Tabi'i].

وَعَنْ سَعِيدِ بْنِ اَلْمُسَيَّبِ ‏-فِي اَلرَّجُلِ لَا يَجِدُ مَا يُنْفِقُ عَلَى أَهْلِهِ‏- قَالَ: { يُفَرَّقُ بَيْنَهُمَا } .‏ أَخْرَجَهُ سَعِيدُ بْنُ مَنْصُورٍ: عَنْ سُفْيَانَ, عَنْ أَبِي اَلزِّنَادِ, عَنْهُ.‏ قَالَ: { فَقُلْتُ لِسَعِيدِ بْنِ اَلْمُسَيَّبِ: سُنَّةٌ? فَقَالَ: سُنَّةٌ } .‏ وَهَذَا مُرْسَلٌ قَوِيَ [1]‏ .‏