Sexual intercourse knowingly interruped in order to avoid pregnancy.
Useful information: It is permissible to perform coitus interruptus, even if it is not mentioned as a condition in the contract. Al-Shahid al-Awwal and al Tabataba'i claim a consensus of the ulama' on this point. They say the consensus derives from a hadith reported from the Imam Ja'far: 'That [semen] belongs to the man: he may expend it as he wishes.' In addition, in contrast to permanent marriage, the basic aim of mut'a is enjoyment, not the production of offspring.
If the woman becomes pregnant such that the pregnancy derives from the period of mut'a, the child belongs to the husband, even if he performed coitus interruptus. This statute applies to every legitimate act of sexual intercourse, not specifically to mut'a, since the principle enunciated in the saying: 'The child belongs to the bed' is of general application.Al-Shaykh Muhammad al-Hasan claims consensus on this point.
However, if the man should deny the child, then it does not belong to him; the 'sworn allegation' required in permanent marriage is not necessary. Al-Shahid al Thani, al-Shaykh al-Ansari and al-Shaykh Muhammad al-Hasan claim consensus on this question. They point out that the 'bed of mut'a', like the 'bed of a slave-girl', does not hold the same high position as the bed of a permanent wife, since a wife by mut'a is a 'rented woman'. On this point two hadith have been recorded.