Mishkat al-Masabih 2695
Abu Rafi‘ said:
God’s messenger married Maimuna when he was not in the sacred state and cohabited with her when he was not in the sacred state, and I was the messenger between them. 

Ahmad and Tirmidhi transmitted it, the latter saying that this is a hasan tradition.
قَالَ: تَزَوَّجَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَيْمُونَةَ وَهُوَ حَلَالٌ وَبَنَى بِهَا وَهُوَ حَلَالٌ وَكُنْتُ أَنَا الرَّسُولَ بَيْنَهُمَا. رَوَاهُ أَحْمَدُ وَالتِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ حَسَنٌ