Gather some men of your family so that I should talk to them. He ('As'as) sent a messenger to them (to the members of his family). When they had assembled, Jundab came there with a yellow hooded cloak on him, He said: Talk what you were busy in talking. The talk went on by turns, till there came his (Jundab's) turn. He took off the hooded cloak from his head and said: I have come to you with no other intention but to narrate to you a hadith of your Apostle: Verily the Messenger of Allah (ﷺ) sent a squad of the Muslims to a tribe of the polytheists. Both the armies confronted one another. There was a man among the army of polytheists who (was so dashing that), whenever he intended to kill a man from among the Muslims, he killed him. Amongst the Muslims too was a man looking forward to (an opportunity of) his (the polytheist's) unmindfulness. He (the narrator) said: We talked that he was Usama b, Zaid. When he raised his sword, he (the soldier of the polytheists) uttered:" There is no god but Allah," but he (Usama b. Zaid) killed him. When the messenger of the glad tidings came to the Apostle (ﷺ) he asked him (about the events of the battle) and he informed him about the man (Usama) and what he had done He (the Prophet of Allah) called for him and asked him why he had killed him. He (Usama) said: Messenger of Allah, he struck the Muslims and killed such and such of them. And he even named some of them. (He continued): I attacked him and when he saw the sword he said: There is no god but Allah. The Messenger of Allah (ﷺ) said: Did you kill him? He (Usama) replied in the affirmative. He (the Holy Prophet) remarked: What would you do with:" There is no god but Allah," when he would come (before you) on the Day of Judgment? He (Usama) said: Messenger of Allah, beg pardon for me (from your Lord). He (the Holy Prophet) said: What would you do with:" There is no god but Allah" when he would come (before you) on the Day of Judgment? He (the Holy Prophet) added nothing to it but kept saying: What would you do with:" There is no god but Allah," when he would come (before you) on the Day of Judgment?
Sahih Muslim Book 1, Hadith 185
“The Messenger of
Allah
(ﷺ) sacrificed two rams on the Day of ‘Eid. When he turned
them
to face towards the prayer direction he said: ‘Verily, I have
turned my face towards Him Who has created the heavens and the earth,
as a monotheist, and I am not of the polytheists. Verily, my prayer,
my sacrifice, my living, and my dying are for Allah, the Lord of all
that exists. He has no partner. And of this I have been commanded,
and
I am the first of the Muslims. O Allah, from You
to
You, on behalf of Muhammad and his nation.’”
Sunan Ibn Majah Book 26, Hadith 2
"Whoever would like to meet Allah tomorrow (i.e. on the Day of Judgment) as a Muslim, let him preserve these five (daily) prayer when the call for them is given, for they are part of the ways of guidance, and Allah prescribed the ways of guidance to your Prophet. By Allah, if each of you prays in his house, you will have abandoned the Sunnah of your Prophet, and if you abandon the Sunnah of your Prophet you will go astray. I remember when no one stayed behind from the prayer except a hypocrite who was known for his hypocrisy. I have a man coming supported by two others, until he joined the row (of worshippers). There is no man who purifies himself and does it well, and comes to the mosque and prays there, but for every step that he takes, Allah raises him in status one degree thereby, and takes away one of his sins."
Sunan Ibn Majah Book 4, Hadith 43