The statement of Umar bin Al Khattab “Those which are in separate flocks are not to be brought together and those which are in one flock are not to be separated” means Two persons had forty goats each ; when the collector came they brought them together in one flock so that only one goat could be given. The phrase “those which are in one flock are not to be separated” means If two partners possessed one hundred and one goats each, three goats were to be given by each of them. When the collector came they separated their goats. Thus only one goat was to be given by each of them. This is what I heard on this subject.  

أَنْ يَكُونَ لِكُلِّ رَجُلٍ أَرْبَعُونَ شَاةً فَإِذَا أَظَلَّهُمُ الْمُصَدِّقُ جَمَعُوهَا لِئَلاَّ يَكُونَ فِيهَا إِلاَّ شَاةٌ وَلاَ يُفَرَّقُ بَيْنَ مُجْتَمِعٍ أَنَّ الْخَلِيطَيْنِ إِذَا كَانَ لِكُلِّ وَاحِدٍ مِنْهُمَا مِائَةُ شَاةٍ وَشَاةٌ فَيَكُونُ عَلَيْهِمَا فِيهَا ثَلاَثُ شِيَاهٍ فَإِذَا أَظَلَّهُمَا الْمُصَدِّقُ فَرَّقَا غَنَمَهُمَا فَلَمْ يَكُنْ عَلَى كُلِّ وَاحِدٍ مِنْهُمَا إِلاَّ شَاةٌ فَهَذَا الَّذِي سَمِعْتُ فِي ذَلِكَ