Ibn 'Umar (May Allah be pleased with them) reported:
Whenever we took a pledge of allegiance to Messenger of Allah ﷺ to hear and obey, he ﷺ would say to us, "As far as you are capable of."

[Al-Bukhari and Muslim].

وعنه قال: كنا إذا بايعنا رسول الله ﷺ على السمع والطاعة يقول لنا: “فيما استطعتم” ((متفق عليه))