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]. (ID)
Arabic/English book reference (ID): Book 1, Hadith 664 (ID)