Reference for Rosh Hashanah 9:7

אמר רב חסדא פסח כדי נסבה

Has not a Master said, It is a mizwah to count days and it is also a mizwah to count weeks?<span class="x" onmousemove="('comment',' To say, e.g., 'seven days which are one week to the 'omer'.');">¹¹</span> And further, we read in the text, 'the feast of weeks'.<span class="x" onmousemove="('comment',' Deut. XVI, 16.');">¹²</span>

Jastrow