Kaab bin Malik reported,

Regarding the account of his staying behind from the expedition of Tabuk and Allah's acceptance of his repentance, the Messenger of Allah ﷺ, his face beaming with joy, said, "Rejoice in the best day that has ever come upon you since the day your mother gave birth to you."I asked, "Is this from you, Messenger of Allah, or from Allah?"He replied, "No, it is from Allah."Then Allah revealed to His Messenger ﷺ, "Allah has certainly turned in mercy to the Prophet and the Emigrants..." up to His words "...and be with the truthful" [Tawba 9:117–119].By Allah, after Allah guided me to Islam, no blessing He has bestowed upon me has been greater in my own estimation than my truthfulness with the Messenger of Allah ﷺ, that I did not lie to him and so perish as those who lied perished. The hadith continues.

عن كعب بن مالك قال

- في قصة تخلفه عن غزوة تبوك وتوبة الله عليه- قال رسول الله ﷺ وهو يبرق وجهه من السرور: أبشر بخير يوم مر عليك يوم ولدتك أمك قال: قلت: أمن عندك يا رسول الله أم من عند الله؟ قال: لا، بل من عند الله. قال: وأنزل الله على رسوله ﷺ: {لقد تاب الله على النبي والمهجرين} إلى قوله {وكونوا مع الصدقين} [التوبة: ١١٩]. قال: فو الله ما أنعم الله علي من نعمة قط بعد أن هداني للإسلام أعظم في نفسي من صدقي لرسول الله ﷺ أن لا أكون كذبته، فأهلك كما هلك الذين كذبوا، الحديث.