"And those who are steadfast in their testimonies," meaning testimonies regarding matters between people, which they uphold when they possess them.
﴿وَالَّذين هم بشهاداتهم قائمون﴾ وَهِيَ شَهَادَاتٌ فِيمَا بَيْنَ النَّاسِ يقومُونَ بهَا إِذا كَانَت عِنْدهم