I gave the pledge of allegiance to Allah's Messenger (ﷺ) for the following:

1. offer prayers perfectly

2. pay the Zakat (obligatory charity)

3. and be sincere and true to every Muslim.
Sahih al-Bukhari Book 2, Hadith 50
← Previous Hadith Allah's Messenger (ﷺ) said, "You will be rewarded for whatever you spend for Allah's sake even if it were a morsel which you put in your wife's mouth."

Sahih al-Bukhari Book 2, Hadith 49 Next Hadith → I heard Jarir bin 'Abdullah (Praising Allah). On the day when Al-Mughira bin Shu'ba died, he (Jarir) got up (on the pulpit) and thanked and praised Allah and said, "Be afraid of Allah alone Who has none along with Him to be worshipped.(You should) be calm and quiet till the (new) chief comes to you and he will come to you soon. Ask Allah's forgiveness for your (late) chief because he himself loved to forgive others." Jarir added, "Amma badu (now then), I went to the Prophet and said, 'I give my pledge of allegiance to you for Islam." The Prophet (ﷺ) conditioned (my pledge) for me to be sincere and true to every Muslim so I gave my pledge to him for this. By the Lord of this mosque! I am sincere and true to you (Muslims). Then Jarir asked for Allah's forgiveness and came down (from the pulpit).

Sahih al-Bukhari Book 2, Hadith 51