As salaam alaeykum warahmatullah. Is it permissible to seek help from a non-Muslim whom one fears that he might later use that to insult Islam? As in, he might be saying in the future that he has helped him while his fellow Muslims didnt, and thus, insulting them and Islam.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

In general, it is permissible for a Muslim to seek the help of a Kaafir (non-Muslim) and the Prophet hired ‘Abdullah ibn Urayqit to guide him on the road in Hijrah (migration) while he (‘Abdullah) was a polytheist at the time.

The jurists detailed in their books the circumstances when it is permissible for a Muslim to seek the help of a non-Muslim, and when it is not permissible.

The Fiqh Encyclopedia reads:

“It is permissible to seek the help of a non-Muslim in general, whether he is from the People of the Book or others, in matters other than acts of obedience, such as in learning writing, calculation, permissible poetry, and in building bridges, houses, mosques and others, if he is not forbidden (in principle) from undertaking such works. However, it is not permissible to seek his help in acts of obedience, such as the Athan, Hajj and teaching the Quran. It is also forbidden to seek his help in matters which he is Islamically forbidden to do, such as making him a ruler over the Muslims, or a person in authority and control over their children. Seeking the help of the People of the Book may be permissible in some matters, such as hunting and slaughtering, but not the help of the polytheist or the Magi, as they are forbidden from undertaking hunting and slaughtering for the Muslim.” [End of quote]

As regards your statement that ‘he might later use that to insult Islam’; if you mean that it is possible that he may remind the Muslim with his favors upon him in the future and boast about the services that he had provided for him, then this is a favor upon the one (Muslim) who sought his help, but it is not an insult to Islam. If someone knows that the non-Muslim will remind him with his favors upon him in the future and boast about the services that he provides for him (the Muslim), then he should not seek his help nor allow him to do a favor for him. Some jurists forbade anything that would lead a non-Muslim to do an act of benevolence (kindness) to the Muslim. ‘Aleesh, from the Maaliki School of jurisprudence, said while enumerating the reasons for the prohibition of the non-Muslim attending the funeral procession of a Muslim:

“The non-Muslim attending the funeral procession of a Muslim is considered an act of kindness to the Muslim, while Allah Says (what means): {…and never will Allah give the disbelievers over the believers a way [to overcome them].} [Quran 4:141]” [End of quote]

Allah knows best.