Sahih Muslim 8456
In-book no 1179وَحَدَّثَنَاهُ يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا فُضَيْلُ بْنُ عِيَاضٍ، عَنْ مَنْصُورٍ، بِهَذَا الإِسْنَادِ وَقَالَ " فَلْيَتَحَرَّ الَّذِي يُرَى أَنَّهُ الصَّوَابُ " .
This hadith has been reported by Mansur with the same chain of transwitters and he said: " He should aim at what is according to him correct."