Reward of bearing witness that there is no God except Allah

1. My father رحمه الله said: it was narrated to me by Abdillah b. al-Hassan Mu’addab from Ahmad b. Ali al-Asbahani from Ibrahim b. Muhammad al-Thaqafi from Muhammad b. Yahya from Muhammad b. Ishaq from Abi Harun al-’Abdi from Abi Sa’eed al-Khudri who said: The Messenger of Allah صلى الله عليه وعلى آله وسلم was sitting on a certain day, and with him were some of his companions, among them Ali ibn Abi Talib عليه السلام. So he صلى الله عليه وعلى آله وسلم said, "Whoever says 'La ilaha illallah' (there is no god but Allah) shall enter Paradise." Two men from his companions said, "We say 'La ilaha illallah'". The Messenger of Allah صلى الله عليه وعلى آله وسلم replied, "The testimony of 'There is no god but Allah' is accepted only from this person and his Shia (followers) who have taken the covenant of our Lord." The two men said, "We say 'La ilaha illallah'". Then the Messenger of Allah صلى الله عليه وعلى آله وسلم placed his hand on the head of Ali عليه السلام and said, "The sign (of acceptance of the statement of La ilaha illallah) is that one should not break oaths given to him, nor sit in his place or reject his words."