What is the evidence regarding the duration of shortening prayers during a settled stay?

Primary text

The evidence supporting shortening prayers is the narration from Anas that the Prophet set out with them to Mecca and shortened prayers until his return, staying in Mecca for ten days while shortening the prayers (agreed upon by Bukhari and Muslim). Furthermore, evidence from Jabir and Ibn Abbas indicates the Prophet shortened prayers for several days upon arriving in Mecca, including the days from the fourth to the seventh. If one intends to stay as the Prophet did during that time, one shortens; if one intends to stay longer, one completes. This suggests that staying for twenty-one prayers, which exceeds four days, warrants shortening, contradicting the view limiting the period to four days.