This hadith has been narrated on the authority of Abu Bishr with the same chain of transmitters (with a slight variation of words and these are), that he (the narrator) said:" During any month continuously since he came to Medina."
وَحَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ وَأَبُو بَكْرِ بْنُ نَافِعٍ عَنْ غُنْدَرٍ عَنْ شُعْبَةَ عَنْ أَبِي بِشْرٍ بِهَذَا الْإِسْنَادِ وَقَالَ شَهْرًا مُتَتَابِعًا مُنْذُ قَدِمَ الْمَدِينَةَ
Muslim
The Book of Fasting • Hadith 231