According to the prophecy, the eighth child of Devaki would kill Kamsa

Expressions researched:
"According to the prophecy" |"Kamsa that the child who would kill him" |"Kamsa would be killed by the eighth child of Devaki" |"Kaṁsa would be killed" |"the eighth child of Devaki would kill him" |"the eighth child of Devaki" |"would kill Kaṁsa"

SB Canto 10.1 to 10.13

Even if Kaṁsa were to see that the eighth child of Devakī was a daughter, he should have no doubt that the eighth child was to kill him.

SB 10.1.34, Translation and Purport:

While Kaṁsa, controlling the reins of the horses, was driving the chariot along the way, an unembodied voice addressed him, "You foolish rascal, the eighth child of the woman you are carrying will kill you!"

The omen spoke of aṣṭamo garbhaḥ, referring to the eighth pregnancy, but did not clearly say whether the child was to be a son or a daughter. Even if Kaṁsa were to see that the eighth child of Devakī was a daughter, he should have no doubt that the eighth child was to kill him. According to the Viśva-kośa dictionary, the word garbha means "embryo" and also arbhaka, or "child." Kaṁsa was affectionate toward his sister, and therefore he had become the chariot driver to carry her and his brother-in-law to their home. The demigods, however, did not want Kaṁsa to be affectionate toward Devakī, and therefore, from an unseen position, they encouraged Kaṁsa to offend her. Moreover, the six sons of Marīci had been cursed to take birth from the womb of Devakī, and upon being killed by Kaṁsa they would be delivered. When Devakī understood that Kaṁsa would be killed by the Supreme Personality of Godhead, who would appear from her womb, she felt great joy. The word vahase is also significant because it indicates that the ominous vibration condemned Kaṁsa for acting just like a beast of burden by carrying his enemy's mother.

According to the prophecy, the eighth child of Devakī would kill Kaṁsa, and therefore when Kaṁsa saw that the eighth child was a female and heard that his so-called enemy had taken birth elsewhere, he was struck with wonder.

SB 10.4 Summary:

After Vasudeva bound himself with iron shackles as before, all the doors of the prison house closed by the influence of Yogamāyā, who then began crying as a newborn child, This crying awakened the doorkeepers, who immediately informed Kaṁsa that a child had been born to Devakī. Upon hearing this news, Kaṁsa appeared with great force in the maternity room, and in spite of Devakī's pleas that the child be saved, the demon forcibly snatched the child from Devakī's hands and dashed the child against a rock. Unfortunately for Kaṁsa, however, the newborn child slipped away from his hands, rose above his head and appeared as the eight-armed form of Durgā. Durgā then told Kaṁsa, "The enemy you contemplate has taken birth somewhere else. Therefore your plan to persecute all the children will prove futile."

According to the prophecy, the eighth child of Devakī would kill Kaṁsa, and therefore when Kaṁsa saw that the eighth child was a female and heard that his so-called enemy had taken birth elsewhere, he was struck with wonder. He decided to release Devakī and Vasudeva, and he admitted before them the wrongness of his atrocities. Falling at the feet of Devakī and Vasudeva, he begged their pardon and tried to convince them that because the events that had taken place were destined to happen, they should not be unhappy for his having killed so many of their children. Devakī and Vasudeva, being naturally very pious, immediately excused Kaṁsa for his atrocities, and Kaṁsa, after seeing that his sister and brother-in-law were happy, returned to his home.

Kaṁsa was very anxiously waiting because of the prophecy that the eighth child of Devakī would kill him.

SB 10.4.2, Translation and Purport:

Thereafter, all the watchmen very quickly approached King Kaṁsa, the ruler of the Bhoja dynasty, and submitted the news of the birth of Devakī's child. Kaṁsa, who had awaited this news very anxiously, immediately took action.

Kaṁsa was very anxiously waiting because of the prophecy that the eighth child of Devakī would kill him. This time, naturally, he was awake and waiting, and when the watchmen approached him, he immediately took action to kill the child.

Since Devakī was a human being, how could the goddess Durgā become her daughter? This was one cause of Kaṁsa's astonishment. Also, how is it that the eighth child of Devakī was a female?

SB 10.4.14, Purport:

Kaṁsa was astonished because the goddess Durgā had become the daughter of Devakī. Since Devakī was a human being, how could the goddess Durgā become her daughter? This was one cause of his astonishment. Also, how is it that the eighth child of Devakī was a female? This also astonished him. Asuras are generally devotees of mother Durgā, Śakti, or of demigods, especially Lord Śiva. The appearance of Durgā in her original eight-armed feature, holding various weapons, immediately changed Kaṁsa's mind about Devakī's being an ordinary human. Devakī must have had some transcendental qualities; otherwise why would the goddess Durgā have taken birth from her womb? Under the circumstances, Kaṁsa, struck with wonder, wanted to compensate for his atrocities against his sister Devakī.

SB 10.4.25, Purport:

Devakī and Vasudeva, both highly elevated personalities, accepted the truth presented by Kaṁsa that everything is ordained by providence. According to the prophecy, Kaṁsa would be killed by the eighth child of Devakī. Therefore, Vasudeva and Devakī saw that behind all these incidents was a great plan devised by the Supreme Personality of Godhead. Because the Lord had already taken birth, just like a human child, and was in the safe custody of Yaśodā, everything was happening according to plan, and there was no need to continue their ill feeling toward Kaṁsa. Thus they accepted Kaṁsa's words.

Krsna, The Supreme Personality of Godhead

Garga Muni intimated to Nanda Mahārāja that the female child was born of Yaśodā and that Kṛṣṇa was born of Devakī and they were exchanged. Also, the female child, Durgā, had informed Kaṁsa that the child who would kill him was already born somewhere else.

Krsna Book 8:

By his astrological calculation, Garga Muni could understand that Kṛṣṇa was the son of Devakī, which Nanda did not know. Indirectly Garga Muni said that Kṛṣṇa and Balarāma were both sons of Vasudeva. Balarāma was known as the son of Vasudeva because His mother, Rohiṇī, was present there, but Nanda Mahārāja did not know about Kṛṣṇa. Garga Muni indirectly disclosed the fact that Kṛṣṇa was the son of Devakī. Garga Muni also warned Nanda Mahārāja that if he would perform the reformatory ceremony, then Kaṁsa, who was naturally very sinful, would understand that Kṛṣṇa was the son of Devakī and Vasudeva. According to astrological calculation, Devakī could not have a female child, although everyone thought that the eighth child of Devakī was female. In this way Garga Muni intimated to Nanda Mahārāja that the female child was born of Yaśodā and that Kṛṣṇa was born of Devakī and they were exchanged. Also, the female child, Durgā, had informed Kaṁsa that the child who would kill him was already born somewhere else. Garga Muni stated, "If I give your child a name and if He fulfills the prophecy of the female child to Kaṁsa, then it may be that the sinful demon will come and kill this child also after the name-giving ceremony. But I do not want to become responsible for all these future calamities."