Hawzah News Agency – Enjoinment of bearing witness:

الإمامُ الصّادقُ عليه السلام - في قوله تعالى :(وَلا يَأبَ الشُّهَداءُا)- : لا يَنبَغِي لِأَحَدٍ إذا ما دُعِيَ للشهادَةِ شَهِدَ علَيها أن يَقولَ: لا أشهَدُ لَكُم.

Imam al-Sadiq (AS) with regards to Allah’s verse in the Qur’an: “The witnesses must not refuse when they are called”, said, ‘When called to bear witness to something that one has indeed witnessed, nobody has the right to say, ‘I refuse to bear witness to you.’

Source: Tafsir al-Ayyashi, v. 1, p. 156, no. 524