The Kursi (footstool) in comparison to the Throne is only like an iron ring thrown in a desert on earth
Authentic hadithعن أبي ذر الغفاري رضي الله عنه مرفوعاً: "ما الكرسي في العرش إلا كحلقة من حديد ألقيت بين ظهري فلاة من الأرض".
Abu Dharr al-Ghifāri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The Kursi in comparison to the Throne is only like an iron ring thrown in a desert on earth."
Explanation
The Prophet (may Allah's peace and blessings be upon him) here says that the Kursi, despite its hugeness, is in comparison to the Throne like an iron ring thrown in a boundless desert on earth. This indicates the greatness and absolute power of its Creator.
Source · Ibn Abi Shaybah in Al-‘Arsh - Adh-Dhahabi in Al-‘Uluww
From the Hadith Encyclopedia (hadeethenc.com).