Muwatta Malik 290

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ أَبِي النَّضْرِ، مَوْلَى عُمَرَ بْنِ عُبَيْدِ اللَّهِ عَنْ بُسْرِ بْنِ سَعِيدٍ، أَنَّ زَيْدَ بْنَ ثَابِتٍ، قَالَ أَفْضَلُ الصَّلاَةِ صَلاَتُكُمْ فِي بُيُوتِكُمْ إِلاَّ صَلاَةَ الْمَكْتُوبَةِ ‏.‏

Yahya related to me from Malik from Abu'n-Nadr, the mawla of Umar ibn Ubaydullah from Yusr ibn Said that Zayd ibn Thabit said, "The most excellent prayer is your prayer in your house, except for the prescribed prayers

Reference

Muwatta Malik 290

In-book

Book 8, Hadith 4