The Prophet (ﷺ) said, "Beware of suspicion (about others), as suspicion is the falsest talk, and do not spy upon each other, and do not listen to the evil talk of the people about others' affairs, and do not have enmity with one another, but be brothers. And none should ask for the hand of a girl who is already engaged to his (Muslim) brother, but one should wait till the first suitor marries her or leaves her."
Sahih al-Bukhari Book 67, Hadith 79
← Previous Hadith The Prophet (ﷺ) decreed that one should not try to cancel a bargain already agreed upon between some other persons (by offering a bigger price). And a man should not ask for the hand of a girl who is already engaged to his Muslim brother, unless the first suitor gives her up, or allows him to ask for her hand.

Sahih al-Bukhari Book 67, Hadith 78 Next Hadith → "When Hafsa became a widow," `Umar said, "I met Abu Bakr and said to him, 'If you wish I will marry Hafsa bint `Umar to you.' I waited for a few days then Allah's Messenger (ﷺ) asked for her hand. Later Abu Bakr met me and said, 'Nothing stopped me from returning to you concerning your offer except that I knew that Allah's Messenger (ﷺ) had mentioned (his wish to marry) her, and I could never let out the secret of Allah's Messenger (ﷺ) . If he had left her, I would have accepted her.' "

Sahih al-Bukhari Book 67, Hadith 80