The offering of two Salat together at Al-Muzdalifa

Narrated Usama bin Zaid:

Allah's Apostle proceeded from 'Arafat and dismounted at the mountainous pass and then urinated and performed a light ablution. I said to him, "(Shall we offer) the prayer?" He replied, "The prayer is ahead of you (i.e. at Al-Muzdalifa)." When he came to Al-Muzdalifa, he performed a perfect ablution. Then Iqama for the prayer was pronounced and he offended the Maghrib prayer and then every person made his camel kneel at his place;
and then Iqama for the prayer was pronounced and he offered the ('Isha') prayer and he did not offer any prayer in between them (i.e. Maghrib and 'Isha' prayers).

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ كُرَيْبٍ، عَنْ أُسَامَةَ بْنِ زَيْدٍ ـ رضى الله عنهما ـ أَنَّهُ سَمِعَهُ يَقُولُ دَفَعَ رَسُولُ اللَّهِ ﷺ مِنْ عَرَفَةَ، فَنَزَلَ الشِّعْبَ، فَبَالَ ثُمَّ تَوَضَّأَ، وَلَمْ يُسْبِغِ الْوُضُوءَ. فَقُلْتُ لَهُ الصَّلاَةُ. فَقَالَ " الصَّلاَةُ أَمَامَكَ ". فَجَاءَ الْمُزْدَلِفَةَ، فَتَوَضَّأَ، فَأَسْبَغَ، ثُمَّ أُقِيمَتِ الصَّلاَةُ، فَصَلَّى الْمَغْرِبَ، ثُمَّ أَنَاخَ كُلُّ إِنْسَانٍ بَعِيرَهُ فِي مَنْزِلِهِ، ثُمَّ أُقِيمَتِ الصَّلاَةُ فَصَلَّى، وَلَمْ يُصَلِّ بَيْنَهُمَا.