Sahih Muslim , Book 13, Hadith 206 (In-Book) ⓘ
This hadith has been narrated on the authority of Sufyan with the same chain of transmitters in which it is said: " Fasting of two months."
وَحَدَّثَنِيهِ إِسْحَاقُ بْنُ مَنْصُورٍ، أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ سُفْيَانَ، بِهَذَا الإِسْنَادِ وَقَالَ صَوْمُ شَهْرَيْنِ .
also referenced under: Hadith 1149 (Reference) & Book 6, Hadith 2560 (USC-MSA)