When he was young he was captured after a nearby tribe attacked his family tribe, Bani Maa’n and was sold in the market of ‘Ukaad. His parents looked for him everywhere and could not find him. He was sold to Hakim Ibn Huzam, Hakim then gave Zaid as a gift to his aunt called Khadijah bint Khawylid (may Allah have mercy upon her). Khadijah then gave Zaid as a gift to her husband Muhammad ibn Abdullah who loved Zaid dearly.
The grief of Zaid’s parents came to an end when members of his family’s tribe bumped into Zaid. Zaid ibn Harith (may Allah have mercy upon him) left a message with them to tell his parents that he is fine and lives with a loving father. Once his father heard the message, he prepared for his travel to Makkah. He asked for Prophet Muhammad (peace and blessings be upon him) upon his arrival and thanked him and his tribe for their security, generosity, care and help followed by asking for his son and the ransom required.
The Prophet (peace and blessings be upon him) was attached to Zaid (May Allah have mercy be upon him) but he also respected Haritha’s parental right. He then asked Zaid to make a choice between them.
In response, Zaid (may Allah have mercy upon them) refused to make a choice and said Prophet Muhammad (peace and blessings be upon him) is a father and uncle. The eyes of the Prophet Muhammad (peace and blessings be upon him) were filled with tears. He then took his hand and went to the Kaaba and shouted with gratefulness and compassion:
“I bear witness that Zaid is my son, and in case I die first, he will inherit from me, and in case he dies first, I will inherit from him."
From that moment, he was known as Zaid ibn Muhammad. Haritha was happy that his son will be looked after by Prophet (peace and blessings be upon him) and returned back to Bani Maa’n.
When the first revelation revealed upon Prophet (peace and blessings be upon him), Zaid embraced Islam immediately because he trusted the Prophet (peace and blessings be upon him)
"Surely, the most honorable among you in the sight of Allah are the most pious of you " Surah Al-Hujurat [verse 13].
Due to his love for Zaid, he married his cousin Zainab to him but the distance between them grew like the mountains of Safa and Marwa. He wanted to divorce her and Prophet Muhammad (peace be upon him) failed to keep their marriage going and ended up in divorce. Zaid later married Umm Kulthum bint ‘Uqbah whom he had a son called Usamah.
The Prophet (peace and blessings be upon him) was ordered to marry Zainab to ensure Zaid was not the son of Prophet (peace and blessings be upon him). His sons died at childhood and Allah (The Most Wise) wanted to declare that Prophet Muhammad (peace and blessings be upon him) was the last messenger for if he had a son, he would inherit Prophethood just like in the case of Zakaria and Yahya (may Allah grant them mercy). Gossip grew and Zaid was renamed after his father again ‘Zaid ibn Haritha’.
“And when you said to him to whom Allah had shown favour and to whom you had shown a favor: Keep your wife to yourself and be careful of (your duty to) Allah; and you concealed in your soul what Allah would bring to light, and you feared men, and Allah had a greater right that you should fear Him. But when Zaid had accomplished his want of her, We gave her to you as a wife, so that there should be no difficulty for the believers in respect of the wives of their adopted sons, when they have accomplished their want of them; and Allah's command shall be performed.” (Surah A-Ahzaab, Verse 37)
"Mohammed is not a father of any man among you, but he is the Messenger of Allah and the last of the Prophets " (Surah Al-Ahzaab, 90)
Zaid was amongst those who played a crucial role in spreading the words of peace of Islam. Zaid fought many battles, amongst them was Battle of Badr. He was the commander of various battles such as Al-Tarf, Al-I’is and Al-Hismi. He was not looking for victory, rather he was thinking of Jannah. He was appointed the first leader in the battle of Mut’ah and it was the last battle. The Prophet peace and blessings be upon him chose him over his close friend Jaffar ibn Abu Talib to be the first commander. If he was injured or killed, Jaffar would be the next leader and if Jaffar was martyred then Abdullah ibn Rawaha would become the leader. Zaid was always prepared and saw each day as his last. All three commanders passed away and Khalidibn Waleed took the flag. Prophet (peace and blessings be upon him) cried and remembered his serene smile.
His love for Zaid was so strong that Zaid’s son, Usamah, who was 20 years old at the time, was the head of the army where the closest companions of the Prophet (peace and blessings be upon him) were present as soldiers, for instance, Abu Bakr ibn Siddiq and ‘Umar ibn Khattab. Many were shocked and when the gossip reached to Prophet (peace and blessings be upon him), he defended his decision and said he deserves to be commander just like his father Zaid and requested that Usamah should be treated well.
Its amazing how someone who was kidnapped became so beloved to the Prophet Muhammad (peace and blessing be upon him) that he even called him his son. The humbleness and compassion that the Prophet Muhammad (peace and blessings be upon him) had. He abolished discrimination and loved Zaid for being him. His personality. Love has no borders.
Source: Suwar min Hayat al-Sahaba by Dr. Abdul-Rahman Ra'fat al-Basha.